Pages: [1] 2   Go Down

Author Topic: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)  (Read 655 times)

N4KMG

  • Member
  • Posts: 1
W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« on: August 20, 2022, 12:28:01 PM »

It took me a while to post this because I wanted to give Tim Fields W4HRK the opportunity to make things right.

On Friday, September 10, 2021, I met Tim Fields in Gate City, Virginia, to trade my mint Alpha 86 plus $3500 cash for his "mint" Alpha 77SX. He seemed like a very genuine fella when I met him and he told me the Alpha 77SX was in perfect working order and I would be VERY happy with it when I got back home. To my horror, when I got home, the unit was not in mint condition (mechanically) at all.

See the detailed invoice from Dick Byrd and all the repair work he did right after my purchase. I asked for W4HRK to at least help with a partial payment for the invoice and his reply was "it worked perfectly when it left my house". No matter what his reply may be to this complaint, it is just not very ethical in the way he treated me. He has not replied to any further attempts of communication. Dick Byrd will validate everything I have communicated here.

Invoice
October 10, 2021

Richard Byrd
3853 Willow Ridge Ct.
Douglasville, GA 30135
Checks payable to Richard Byrd
PayPal account: SERVICE@N4UQ.COM

Wes Wingo, N4KMG
3051 Nunally Springs Rd.
Good Hope, GA 30641
770-601-1452
wes.wingo@gmail.com
Repairs to Alpha 77 Serial number 2974:
Diagnosed client complaint of low output.
Restored transformer connector to factory standard.
Fabricated and installed a wattmeter PC board.
Tested on all hf HAM bands and provided documentation.
Replaced Step-start relays &Installed rear panel step-start fuses.
Cleaned up all the primary wiring.
Fixed linkage on the TUNE capacitor and crank assembly.
Replaced (inside) LOAD capacitor and calibrated load knob.
LED meter kit. $24.00
1 LOAD capacitor, Oren Elliott $169.00
Connector shells and pins $5.00
2 HEan 24-V Panasonic step-start relays $49.00
2 panel mount fuse holders $26.00
2 2.5A slow-blow fuses $4.00
2 BLN25A fuses $23.00
Wattmeter parts $25.00
Labor, 6 hours $600.00

Total $925.00

73 de N4KMG
Wes Wingo
Logged

KM4AH

  • Member
  • Posts: 1615
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #1 on: August 20, 2022, 02:47:11 PM »

I think if you took one straight out of the box and sent it to Dick Byrd he would do $900 worth of "repairs".

Would be much more interesting to know what it was not doing when you received it. I ran one for 15 years, they are not particularly complicated.
Logged

W7CXC

  • Member
  • Posts: 336
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #2 on: August 20, 2022, 03:33:02 PM »

Perhaps the guy had very high line voltage and he adjusted taps ( if it has those) to compensate. Were some of those "repairs" actually modifications or upgrades?  Just wondering.
Logged

K4MK

  • Member
  • Posts: 23
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #3 on: August 20, 2022, 04:01:16 PM »

I have a 77SX that I have been using for many years. It works just fine, but as with any 40 year old piece of equipment, it could probably use a good overhaul by an expert (which Dick Byrd is ). I' m not defending the seller and don' t know him, but my thought is that you now have a really nice updated amplifier, and the charges for the work that Dick did are entirely reasonable.
Logged

AE0Q

  • Member
  • Posts: 414
    • AE0Q Amateur Radio
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #4 on: August 20, 2022, 04:23:10 PM »

Fabricated and installed a wattmeter PC board.

Replaced Step-start relays &Installed rear panel step-start fuses.

Fixed linkage on the TUNE capacitor and crank assembly.

Some early 77D amps didn't have a wattmeter board, the wattmeter parts are dead-bug mounted at the RF Out connector.

The stock Stepstart fuses are in fuseholders on the chassis inside the amp, down by the AC relays and inconvenient to reach.

The coupling between the crank shaft and the TUNE vacuum variable comes apart very easily when the amp is moved if the front panel is flexed at all.

And the 77/77D amps only have tap settings for 120 or 240 vac.  There are no intermediate taps to adjust.

As already commented, now you have a really nice 77Sx :-)
Logged
NSGA Edzell 1974-77  CTM2  GM5BKC : NSGA Rota 1972-74   ZB2WZ, SV0WY
https://radioandtravels.blogspot.com/
http://www.qsl.net/ae0q/

KA4WJA

  • Posts: 1601
    • HomeURL

Wes,
I'm sorry you were disappointed in your purchase....as a fellow ham, I do feel for you.
As an Alpha owner (two 77Sx's --- one factory Sx and one "conversion" Sx....and an Alpha 78), perhaps I can add some clarity / context that might help?
I do NOT work for Alpha....just a happy customer!  :)
And, I love Dick Byrd....a super good guy!  :)

BTW, I do not know Tim (the seller), but I heard he has some health issues.

When buying any used amp, especially one that has been modified / converted, the buyer needs to do extra research / extra homework, and look closely at the pics...


1)  The linkage of vacuum-variable TUNE cap to the turns-counter dial is actually pretty heavy-duty....but, obviously this cannot safely be a direct connection....and, ironically, this heavy-dutiness can cause an issue in shipping / moving / loading-n-unloading an older amp, as it is ~ 40 years old, and if the vacuum-variable hold-down ring is no longer rigidly-tight, if you press hard on the turns-counting handle (like you would, if man-handling the amp in/out of a car, up/down stairs, into/out-of your shack, etc.), it will push back against the vacuum variable and then when you release your pressure the vacuum-variable will stay put (too far back) and extra space will now be opened-up in the mechanical linkage, and now you have slippage and/or no movement at all of the TUNE cap!  {which this alone could account for poor tuning and/or low-output!}

This is a simple, and very easy-peasy "repair"....takes a Phillips screwdriver....but you do need to open up the RF Deck to access the vacuum-variable, loosen its mounting screw a TINY bit, push it forward against the turns-counter mechanical linkage, and tighten it down...close everything back up and you're good-to-go!

Lots of screws to deal with, to access the RF Deck, but other than that, it'll take you all of 30 seconds to do this "repair".  :)   


2)  As for specifics of your amp, I'm fairly certain that Tim's two-holer 77 (like most out there) was a conversion.  (some, like those that N4UQ did years ago, are so well done they're better than a factory 77Sx....but some can be mediocre)

I never saw Tim's, but assume you looked at internal pics, before making an offer?  (but, perhaps there are somethings that you were not aware to look for....like the watt-meter board on the rear-panel / output connector, just above the vacuum T/R relay....whether it had 160m?  whether any tank circuit changes / adjustments had been made?  and, more importantly were there any pics of the load caps, to see if it had been overloaded/arc'ed if mis-tuned, especially mis-tuned on the low-bands?)

Also, please be aware that no matter what the lore (and the internet) says, while 77Sx is a 4kw amp, with an internal transformer, it is power-supply-limited!  :(

That means, depending on the band and your AC Mains voltage, if you drive it with only a moderate amount (60 - 70w), it will run WICKED CLEAN (better than any transceiver connected to it, except for a pre-distortion-equipped ANAN or a MkV in Class A w/o any ALC)....and you can lay the "brick-on-the-key" with 3kw out (into a dummy load, of course)!

BTW, one of my 77Sx's (the conversion) was burned-in at the factory at 2kw carrier out for 24 hours straight, when the guy I bought it from sent it in to be cleaned/tested/adjusted before he put it on the market...I spoke with Gordon and Molly about this amp personally, and Molly confirmed 2kw out for 24hrs, and she mentioned that they did that with the factory Sx's too....that was over 20 years ago... (but I didn't buy 2nd Sx / my factory Sx, until last year, so that wasn't anything I cared about at the time).

The reason I mention the above is that, depending on what band and depending on your AC Mains voltage (and depending a little bit on the exact internal transformer you have) if you drive a good 77Sx (conversion or factory) with 85 - 100 watts you can get ~ 4kw+ out, but your HV will be sagging, and this would be for SSB or CW, not "brick-on-the-key" RTTY (power-supply-limited)....and, some hams are "sold" on a 77Sx as a "5kw amp", which it can be with the outboard HV plate transformer, but NOT with the internal transformer!   {depending on what your expectations were, and on how your 77's conversion was done....this could also be a cause of lower than expected output...}

And, while I've never driven it with more than ~ 90w, I have heard (and it does make sense) if you try to drive it harder (> 100 watts of drive) you'll be sagging the HV more, and the IMD worsens...although I was told that at ~ 5kw it's still better than most modern rigs and/or any SS amp....but, again understand that I've never done that, and never will!  (I'm an IMD fanatic, you know!)

(yes, there are Youtube videos showing 5kw out from a 77Sx with the internal transformer, but this is ONLY for SSB rag-chewing service not 100% duty-cycle, and this is ONLY using a "special higher-voltage / lower-current" internal transformer....providing ~ 5000vdc...and this requires upgrades of the both the rectifier and HV filter cap, AND usually requires the user to buy two 3CPX1500 tubes, or take a big chance that they'll not flash-over a 8877....and, then after 1000's of $ all you get is a 5kw SSB rag-chew amp, rather than a "brick-on-the-key" amp!)  Makes no sense to me, but some have done this. :(


3)  And further specific to your amp, I assume it was a conversion from an older 77D not a 77Dx?

(not that big of a deal, but the Dx added 160m and I think there were some other minor tank circuit changes in the "x" models that permitted fairly seamless addition of a second 8877, as well as a few other minor changes?....and, I think this is where some lesser informed folks wish to say that adding a second 8877 screws-up the tank circuit, which is slightly true if converting an older 77D as you need to make those changes/upgrades, but not so true if converting a newer 77Dx...might be wrong here, it's been decades since I heard these details.)  As was explained to me, while the 77D and 77Dx were both supposedly designed to have a second 8877....I was told that the D was not actually built specifically for a second tube as the Dx was. (not sure if that was fact, and/or that it applied to all D's and Dx's....but, it does make sense)

If this is the case, and/or with the TUNE cap linkage loose, etc. when you were trying to get "full output", it's possible that this caused some damage to the Load cap?  {and this, could also be a cause of lower than expected output}

So, while it is a shame that you were not originally happy with your purchase, I think this may actually clear up some conversion confusion....


4)  Upgrading / changing / moving the step-start relays and/or their fuses is not a "repair", it's an upgrade....(and, while I'd do it too, if I was doing other work/repairs, it's not a "repair")

Adding the watt meter board is also an important upgrade from a 77D....but, again, not really a "repair"...

Not sure why the transformer connector was "non-standard"?  But, here again, this goes back to the type of "conversion" done, and could've been seen in internal pics, prior to purchase.


5)  So, other than the minor "repairs" like the quick adjustment of the TUNE cap / turns-counter linkage and changing the transformer connector....the replacement of the loading cap, looks like the only real serious "repair" needed, the rest are additional upgrades that you unfortunately were not aware had not been done when the "conversion" was done....and, we (not anyone here, or even yourself) are not sure if the turns-counter / TUNE cap linkage looseness was the proximate cause of the load cap issue / lower than expected output issue. 

Oh, and don't underestimate the TIME it takes to disassemble / reassemble the 77, as well as replace a few items...
And, I personally think Dick's labor rates are a bit low (damn, don't tell him I said that!)


So, while as I wrote up front I do feel for you....but...

But, you were buying a 40+ year old amp, that you knew had been modified / converted (and you sought it out for that reason), perhaps a bit more research on your part (and some care and inspection prior to powering it up)....and a bit more communication between the seller and yourself (like internal pics...lots of them)....would've eliminated most of these issues, and allowed both parties to be happy with the transaction?
So, taking into account all the above additional info / clarifications, I'd cautiously side with Tim (the seller)....unless he lied to you about something specific, to be a good gentleman and  follow Good Amateur Practice, I'd say he might owe you a polite apology...(and maybe offer to pay 50% of the cost of Load Cap [$84/50], that's what I would do...).


I do hope I helped?   (and say Hi to Dick from me....he's a wicked great guy!)

73,
John,  KA4WJA
« Last Edit: August 22, 2022, 12:29:02 AM by KA4WJA »
Logged

KM4AH

  • Member
  • Posts: 1615
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #6 on: August 22, 2022, 07:34:35 PM »

I still see no reason to believe that it did not work perfectly when it left his house.

What was it not doing. Seem to be hearing a lot of speculation.  From the sellers house to the buyers house to Dick Byrds house.

And, Dick Byrd will validate that it was broke when he got it.
Logged

KA4WJA

  • Posts: 1601
    • HomeURL
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #7 on: August 23, 2022, 04:50:22 PM »

Randy,
I tend to agree with you here.
Although "perfectly" is a subjective word.

I still see no reason to believe that it did not work perfectly when it left his house.

What was it not doing. Seem to be hearing a lot of speculation.  From the sellers house to the buyers house to Dick Byrds house.

And, Dick Byrd will validate that it was broke when he got it.

One of the reasons I provided the details, above, of some of the issues raised here by Wes, was so he (and everyone) will understand the 77Sx better, AND understand that "internet myths" abound.
So, everyone should really do their homework!   (can't believe that anyone spending ~ $5k would do so without more than casual diligence, but when you hear some of the BS that is bandied-about on-the-air and on-line, it makes me wonder)


Still hoping that Wes will stop in here and clarify some things....but oh well?


73 to all,

John,  KA4WJA 
Logged

KM4AH

  • Member
  • Posts: 1615
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #8 on: August 23, 2022, 06:20:08 PM »

Randy,
I tend to agree with you here.
Although "perfectly" is a subjective word.

I still see no reason to believe that it did not work perfectly when it left his house.

What was it not doing. Seem to be hearing a lot of speculation.  From the sellers house to the buyers house to Dick Byrds house.

And, Dick Byrd will validate that it was broke when he got it.

One of the reasons I provided the details, above, of some of the issues raised here by Wes, was so he (and everyone) will understand the 77Sx better, AND understand that "internet myths" abound.
So, everyone should really do their homework!   (can't believe that anyone spending ~ $5k would do so without more than casual diligence, but when you hear some of the BS that is bandied-about on-the-air and on-line, it makes me wonder)


Still hoping that Wes will stop in here and clarify some things....but oh well?


73 to all,

John,  KA4WJA

I probably just have a bad attitude.  I got burnt by an eBay buyer who said a TS950 SD was damaged in shipping and made a PayPal claim.  I refunded his  money and told him to just keep it. I can tell you that the only way UPS could have done the damage is if they ran over it.  He dropped it unpacking it is what happened. Lot of radio for an 80 year old man.

I'm just curious is all. I am no genius by any stretch, but there is nothing on a 77SX I can't fix.
This new stuff, not so much.
Logged

N2MIR

  • Member
  • Posts: 21
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #9 on: August 24, 2022, 07:41:19 AM »

I know it’s to late but my question is why didn’t you take the unit to someone with a test bench befor the switch? In this world today no one can be trusted by just their word. The Ham fests I attended in the past usually have a tech to perform tests on potential equipment sale or trade. To many uneducated ignorant fools out there who damage electronic equipment and then pass them on to others.
Logged

KC0W

  • Member
  • Posts: 1542
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #10 on: August 24, 2022, 04:59:06 PM »

 One post never to be heard from again...............Don't waste your time asking him any questions or making any recommendations.

                                                                Tom KH0/KC0W
Logged

KA4WJA

  • Posts: 1601
    • HomeURL
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #11 on: August 24, 2022, 08:31:59 PM »

Will,
1)  I think Tom, KC0W, has it right....it's not too likely that we'll hear much back from Wes (N4KMG).   As, it's likely he didn't do his homework, and/or didn't look inside and check everything out before powering it up / trying to use it, and ended up learning the hard way.  :(
{and, I feel sorry for Tim, as he is being taken to task for no real reason}


2)  But, to your point about "taking it to someone with a test bench", I'd like to offer some clarification for you.  :)

I know it’s to late but my question is why didn’t you take the unit to someone with a test bench befor the switch? The Ham fests I attended in the past usually have a tech to perform tests on potential equipment sale or trade. 

While this is good generic advice, an Alpha 77Sx is a rather large, heavy, and power-hungry device to be lugging around town in your car/truck, let alone trying to move it through a hamfest!

You see, it is 20" wide x 11" high, x 23" deep  (5" wider and an inch taller, than a full-sized "banker's box", and weighs 105lbs!!!  (and needs 240vac to turn it on)

Now, if shipping (or even just moving it into / out of your car or truck to take it somewhere, hamfest, new owners house, etc.), you of course remove the transformer (49lbs) and ship/transport it separately, so if the amp that Wes was buying was intact with transformer installed, it would've been all but impossible to just "take it to a test bench at a hamfest".  :(


3)  Further complicating this situation are five basic facts:

a)  There were only about 716 (?) of these amps (Alpha 77Dx / Alpha 77Sx) ever built and they haven't been made since 1989 (33 years ago)....they were in production from 1977 - 1989 (with other models preceding and succeeding them, such as the original PA-77 dating back to 1972)  And, they are wicked heavy-duty and reliable, and unless you're an idiot or make some real big error, they are almost bullet-proof and will last many decades more....{while some still find it hard to believe, there is a fairly wide acceptance of the statement: "the 77Dx (or Sx) will be the last amp you'll ever need....unless you want a second one!"....so, this adds to the lore of the "Alpha 77"   Both of mine are now just slightly over 40 years old, and I suspect they will still be running fine 30 more years from now! :) }

b)  The Alpha 77Dx is universally accepted as the best desktop HF ham amp ever made, bar none....and even if compared to larger console amps, is still considered by most hams, to be the best!  They are highly sought after, and retain their value very well...And, will run 1500 - 2000 watts out, 100% duty-cycle, brick-on-the-key, no time-limit, for weeks, etc...from 1.6mhz - 30mhz (except ~ 24mhz)....and ~ 2500 watts out SSB, no time-limit....and, do it all very cleanly, with excellent IMD...and, require pretty-low RF drive from a transceiver, etc...

c)  The Alpha 77Sx (with two 8877 tubes and a slightly larger transformer) as built by the factory (for export only) has a bit more headroom and can output higher power, but is "power-supply-limited".  Usually considered 2000 watts - 2500 watts out 100% duty-cycle, brick-on-the-key, no time-limit, for weeks, etc...1.6mhz - 30mhz (except ~ 24mhz)...Alpha tested them at factory at 2000 watts out, brick-on-the-key for 24hrs+ [remember, "power-supply-limited"] and ~ 3500 - 4000 watts out SSB, no time-limit....and, do it all, very cleanly, with excellent IMD...

d)  An Alpha 77Sx conversion (a 77Dx, converted to a 77Sx) can be the same as a "factory made" 77Sx....or can be inferior (or in some circumstance, can be a bit superior)....but, this all depends on who did the conversion and how they did it!

e)  There is a good deal of BS and myth surrounding these amps, and unfortunately some hams are sold some BS to get them to spend their money, without knowing 3 of the other facts above ("b", "c", and "d")....and unfortunately many are only partially aware of "a"...so, here you start to see the problem.  Yes?  :(



4)  And, while I'm sure some will think me naive here....I disagree here...in ham radio, if a ham tarnishes his/her reputation it will follow them for life....once their callsign is known as a "lid", or "lair", or "ignorant", etc. etc....it never goes away! 

In this world today no one can be trusted by just their word.
 <snip>
 To many uneducated ignorant fools out there who damage electronic equipment and then pass them on to others.

So, I'll push back on the notion that you cannot trust anyone these days....just like Ronald Reagan said "Trust, but Verify!"  :) 

And, in that context, here are my personal experiences with buying multi-thousand dollar Alpha's..

I bought my first 77Sx sight-unseen, I talked to Molly at Alpha where the amp had just been tested/aligned and burned-in again, and had my non-tech sister look at the outside of it, before giving the previous owner my check (yes, he took my check as payment), and I had my sister and her husband take it to FedEx where they packed it (in multiple boxes) and shipped it to me ~ 2000 miles away!   
I bought my second 77Sx from a local gentleman and was able to inspect it inside and out (but, it was not hooked-up, transformer was out....so, I trusted that it would work)...  But, I was already well informed regarding the 77's, as well as did my homework and practiced due diligence....and, never a regret here!  :)


I hope this clarifies some things....and helps some out?

73,
John,  KA4WJA
« Last Edit: August 24, 2022, 08:36:01 PM by KA4WJA »
Logged

KM4AH

  • Member
  • Posts: 1615
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #12 on: August 25, 2022, 05:38:52 PM »

I ran a 77SX for many years.  I have no idea whether it was factory or an upgrade.
I called Peter Dahl on the phone sometime probably early 90's and bought a 2 amp CCS external plate transformer. I ran it 5 KW out all the time, nightly on 3.898 .
Never had a problem with the amp. But, Eimac made some bad tubes during the period.
I had an original 8877 go cold, so I bought a matched pair from Surplus Sales. That was a mistake.
May be wrong , but I think Eimac dumped the out of tolerance 8877's on Surplus Sales who in turn dumped them on the ham community.

They are a 2500 watt amp on 10 meters.  On 40 or 75 they will do 4KW with 150 watts of drive. With an external 2 amp plate transformer and 4000 volts on the plate they will do 5 KW on 40 or 75 with 150 watts of drive.
No guarantee on tube life , LOL.

Nothing wrong with the original design and components as near as I can tell..  I put a lot of hours on them.
Logged

KD6VXI

  • Member
  • Posts: 1022
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #13 on: August 29, 2022, 04:50:32 AM »

The 80s 8877s, mid to late 80s, where trash.

I had an amplifier that ran 3 of them.  After replacing them under warrantee a few times via Henry Radio in LA, Reid sent 3 x 3CX1200A7s, a new filament transformer and a note that they would not replace them anymore.

Amp ran good after that.  Needed more drive, but that was OK since the Valiant had to be loaded lightly for the 3 x 8877s. 

Not sure if the bad batch(es) went to SSON or not.  I bought all my tubes through Henry until RF Parts became a real thing.  They where in my back yard and had better pricing!

--Shane
WP2ASS
Logged

KA4WJA

  • Posts: 1601
    • HomeURL
Re: W4HRK - Alpha 77 SX Not As Described (Very Disappointed)
« Reply #14 on: August 31, 2022, 08:44:28 AM »

After answering a 77Sx question this morning over on qrz, I came back here to look....and, I found two things... :)

1)  For a "huh?" moment, have a look here at the original poster's latest post.....just makes me shake my head and wonder.  :(

https://www.eham.net/classifieds/598900



2)  Randy, I'm not implying a faulty memory on your part....I just wish to add clarification for everyone here, as most will not see the fact that having the out-board 2amp / 6kva CCS xformer makes a big difference! 

I ran a 77SX for many years.  I have no idea whether it was factory or an upgrade.
I called Peter Dahl on the phone sometime probably early 90's and bought a 2 amp CCS external plate transformer. I ran it 5 KW out all the time, nightly on 3.898 .
Never had a problem with the amp. But, Eimac made some bad tubes during the period.
I had an original 8877 go cold, so I bought a matched pair from Surplus Sales. That was a mistake.
May be wrong , but I think Eimac dumped the out of tolerance 8877's on Surplus Sales who in turn dumped them on the ham community.

They are a 2500 watt amp on 10 meters.  On 40 or 75 they will do 4KW with 150 watts of drive. With an external 2 amp plate transformer and 4000 volts on the plate they will do 5 KW on 40 or 75 with 150 watts of drive.
No guarantee on tube life , LOL.

Nothing wrong with the original design and components as near as I can tell..  I put a lot of hours on them.

I've read this over the years, but this runs contrary to my own personal experiences (current, and over the past 20 some years, with my Alpha 77Sx's)....and contrary to some others I've spoken to over the years....

Here is an old example of someone who thought he could drive the crap outa' a 77Sx (to get to some out goal?), and got complaints of "splattering"...
https://www.eham.net/community/smf/index.php/topic,132161.msg1217083.html#msg1217083


To be clear, I've never heard of anyone actually using ~ 150 watts to drive an Sx with an internal/inboard transformer....and, I've stated this here before, there is no need to do so, and doing so is seriously over-driving the amp (no, 75 watts into each 8877 would not necessarily be over-driving the tubes [kinda' depends on your definition of "over-driving"], but this is over-driving an internal-transformer-equipped Sx)
{heck, when first tuning my original Sx, I was surprised at how much I needed to turn down my TR-7's output, (as I was previously driving a pair of 3-500's) as I had pretty high grid current, etc. when I first started tuning it..} 
So, I caution everyone here, please if you should happen to be lucky enough to acquire a 77Sx, please use caution and do not try driving with more than 100 watts....anymore than that, and you may be causing yourself issues!  (over-driving, flat-topping, HV sag, reduced tube life, etc....are all possible issues)  :(

Of course, what drive levels and output levels I'm referring to here, are for CW/SSB and with the internal / inboard transformer....if someone was using a big outboard plate transformer, there would be significantly less hi-voltage drop/sag (practically none, and usually a bit more to start with), and significantly higher output for same/similar drive powers...

{I'm making no statements of "absolutes" here, and am not arguing wattmeter accuracy and am allowing for wattmeter errors....as example, my 77Sx's output on Bird 43 with 5kw slug shows about 100 watts higher than the Alpha 77's internal wattmeter....and, I have my TR-7 currently set to have a max out of ~ 65 - 70 watts (SSB/CW/RTTY/AM), so my normal drive power of ~ 65 - 70 watts shows the same on a Bird 250w slug and on the TR-7's wattmeter...(and it "pins" using a 50watt slug)....so, while I have no idea how accurate these readings are, they do seem to track...oh, and last summer I mistakenly posted my outputs with ~ 75 watts drive as being with only 65 watts, and the outputs with ~ 85 watts drive as being with ~ 75 watts drive (oppss)....}

a)  Case in point...I currently only use about ~65-70 watts of drive....and on 80m and 40m, I get a very clean 3kw+ out (3200 - 3400), into a dummy load...."brick-on-the-key"...with ~ 80ma - 85ma grid current.  {and, while I haven't used on 20m in a long time, if my memory serves me well I had a bit more grid current there but still had ~ 3kw+ out, into dummy load, with 65 watts drive...}


b)  Further to see what's what, when setting the TR-7's max output (ALC pot) I increased drive to check things....and with ~ 75 - 80 watts of drive, my 77's output is ~ 3700 - 3800 watts (~ 85-90ma grid current)...into dummy load.
And with ~ 85 - 90 watts of drive (still showing about the same on the 250 watt slug and TR-7's meter), my 77's output is ~ 4000 - 4100 watts...(at ~ 100ma grid current)....into dummy load...and, while you can start to see a very slight (0.1db ?) gain compression, at 4 - 4.1kw with 85-90 watts of drive, it is certainly not even close to a 1db compression point....and, is still very clean.


c)  Although, with the internal transformer the 77Sx is "power-supply-limited", I'm fairly certain while more output could be obtained with further increase in drive (and re-tuning/loading, of course), I'm concerned about the IMD increasing, etc....as well as needing to adjust blower voltage resistor to increase cooling air flow, etc....(and no longer being operated in a "brick-on-the-key" situation)....not to mention the resulting < 1db increase hardly seems worth lessening tube life!


d)  Many moons ago (late 70's) I heard an acquaintance with his 77Sx in central Florida (this was my first time I heard one on-the-air, and it became a dream of mine...taking me > 20 years to achieve, and then another ~ 20 years to get my second Sx), by happenstance he was also using a TR-7 and had previously been driving that into a pair of 3-500's, and I still remember him saying he can't run the TR-7 "wide-open" or he'd "overdrive the Alpha".....I don't know what his drive level was, no what his output was, but like one of my Sx's his was a "factory Sx", and it worked great for him....

{on side note: his buddies on 75m were chiding him for "spending $6k on an amp!", but then one said "you know, you really don't sound $5k better.....you actually sound $10k better"....of course, this was all "tongue-in-cheek", as the amp certainly didn't make him "sound" any better, just a bit stronger!  But, still remember this almost 45 years on... :) }


3)  So, again, I'm not saying that your memory is faulty....just saying that this is not my experience, and I'd caution others to not drive an Sx (without a big outboard xformer) with much more than 100 watts or so....you shouldn't actually need to do so.  :)



4)  Shane, et al,
Yes, I've heard of the bad run of 8877's....and, while I have no first-hand knowledge/experience with any of those "bad" ones,  I was under the impression (from what I've read over-the-years) that these were from one (or two) production run(s), in the mid-1980's?  :(



5)  Anyway, the original poster seems to be long gone from this thread and is now looking for a tetrode amp (OM Power)...  And, that's his choice....(as weird as it is, to me)

https://www.eham.net/classifieds/598900

Perhaps he just wants to drive the crap out it and splatter all over the band? 
(something that is pretty difficult to do with a 77Sx, even if you mis-tune it....but if you have a FT-857/897 or FT-891/991, etc. you will do a good job splattering with any amp, hi hi....sorry to all with those Yaesu's, I just couldn't resist!)


The real shame here is that Tim, W4HRK, was having his word / reputation questioned, and this just is not cool!


73,
John,  KA4WJA
« Last Edit: August 31, 2022, 09:02:03 AM by KA4WJA »
Logged
Pages: [1] 2   Go Up