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[KA4WJA]

Bob and Jim, Thanks for the additional info.

And, as I suspected....auto-tune, or no-tune SS, is nice to have....and helps keep the rate up if you're doing S&P...but, not an absolute necessity...



1)  Jim, while it was a couple months ago, some friends on 80m (with ANAN's) wanted to try AM for a while (why, I never did grasp)....and, as the TR-7 has "AM-SSB" (full-carrier, but only single-sideband), I switched to AM, adjusted my carrier appropriately, and drove the 77Sx to my normal full PEP output on voice peaks (which would have a carrier power like you mentioned)....BUT...

When was the last time you ran a 1.5 kw CXR  24/7 ?

But, it was for only an hour or two...
I was about to QRT, but they got tired of it as well and called it quits...
My station (even though it's a quick temporary set-up) had no trouble operating like this....not sure if it would do it 24/7 for days on end, but assume it would....but, I do know that I'm not an AM guy, so I'd personally not do it. 




2)  Bob, I love your words here...
While, I've always (since the 70's) known this.....It was 32 years ago that I learned it first hand! 

After making all the preparations, there's nothing worse than to have your amp crap out and ruin your weekend.

Years ago....for the 1990 CQWW 160m CW Contest....I was the tech coordinator for our effort....
I had access to a defunct AM broadcast transmit site in N. Florida (two of the three 190' towers on the ground twisted like pretzels, third tower leaning a tiny bit with some broken guy wires....transmitter building gutted / trashed)...
We used the one remaining tower and ~ 60 of the radials, fed from a Dentron Super Tuner sitting on a cement block at the tower base....and had rigged two beverages (one  ~ 900' beaming NE into EU, and one ~ 700' beaming WNW), using my TR-7's ext rec antenna input...

We knew only one guy locally that had an amp for 160m, a fairly new Ten Tec Titan....we convinced him to let us borrow it....

Just before sunset, about an hour into operating, after working some stations along  US East Coast, some of the magic smoke came out of the amp!   
The band switch burned-up!     
We were hittin' it with ~ 80 watts CW or so, getting ~ 1.5kw - 2kw out, VSWR was flat (Dentron Super Tuner 200' of RG-213 away, at tower base)....that TenTec just didn't like legal-limit+ on 160m CW....

So, we worked the whole contest barefoot....(actually "they" did....I feel ill with some food poisoning....but not a CW op anyway, so after station design, set-up and testing, I was just a "go-for"...)
Think we still won the #4 call area? and placed in the top 10 or so....big tower vertical, lots of radials, a couple beverages, and a TR-7 barefoot....Oh, and some REALLY GREAT CW OPS (retired military CW ops)!!

So, as I wrote above, even though I "knew" what was what, I actually "learned" a lesson that night...

And, btw....since the Titan was almost new....Tentec covered it under warranty!  (and, with the amp in for repair, my friend ended-up exchanging/upgrading it for an Alpha 87!)



Anyway....thanks for the further info....and for reminding me of some fun times. 

73,
John,  KA4WJA 

[KM4AH]

Simplest cure is just move to North Korea.  Then you won't need to worry about tuning to any other frequency than the one you are on.

[AF6D]

John,

Actually it's I that needs to apologize at this point because I see that you took what were really minor complaints on my part so seriously and I regret that. That's my fault for writing that way. I also apologize for my delay in replying. I'm coming off of the death of two family members. I've been a bit preoccupied.

To be honest, my issue wasn't so much with you. It was the audacity of another individual to ask that others "consider the source" because I didn't apologize to you. I couldn't even understand what I was supposed to be apologizing for. 've been called Rob before and it's really not a big issue. I would hate for me speaking out to be the cause for you to be upset. This is amateur radio and some of us like myself can take ourselves too seriously at times.

You did get one thing right. I do tend to approach questions casually. It really is my hope that by asking questions in a relatable way when others come along that are new or less experienced and amateur radio with a similar set of questions about amplifiers they'd be able to come across your very well detailed reply and take what they could use and leave the rest behind. I should have followed my own advice but I guess it was just information overload based on a rude statement by another person. You did make some assumptions and I'm over them. I was over them as soon as I spoke out.

This is a great website and I like it better than Facebook. Facebook spies on people but we'll leave that alone. There are however users that get into ego struggles and I don't want to be one of those people. There are others on this very broad site that see themselves as the all revered guru's and I don't get along with that personality well. For example, I run numerous repeaters that are put together using quality Motorola components or complete builds. I have an entire 12x15 bedroom in my home that is a workshop and is stacked with various types of low loss cable and probably 50 or more Motorola mobiles for linking and this project and that project. Service equipment and the like. But yet I'll go into a Facebook group and some smart ass we'll talk down to me for asking a question that he feels any repeater operator should already know.

I've had to learn a lot of things on my own because Elmer's of the old days just don't seem to exist like they did back then. And yet I will still have people throw things in my face when I ask a simple question and challenge whether or not I should even have repeaters on the air. They go way too far and then when I go look at their license and see they've only been licensed for 3 years it really pisses me off! But you haven't done these things. Not at all.

Bob,
1)  First off, please accept my sincerest and heartfelt apologies....especially for addressing you as "Rob"....it was an erroneous assumption on my part as my older brother "Robert" is called "Rob" (and, you didn't sign any of your posts, so I made a casual mistake and addressed you as Rob rather than Bob), so in addition to my other errors this one is simply a mistake of mine due to a casual assumption. 

I am sorry about this, really I am!

73 (really, best wishes!),
John,  KA4WJA

[KM4AH]

The story I got was the 374A's passband tuning was a series of L networks for each band, plus the manual tuning option.

The story I got was the passband tuning lacked sufficient harmonic suppression to meet the new FCC specs, so the passband tuning concept was dumped on newer alpha amps..... and alpha went to the motorized  tune+load caps and bandswitch.  Dunno how broad the passband tuning was on the 374A, like if into a dummy load.

Both the 78 and 374A use the same Pi-L network on all the bands, they have the Preset tuning bandswitch positions on 80-15m, with different taps on the "Pi inductor" to give broader bandwidth.

We found the "prototype" of the 87A at Alpha 20-odd years ago in boxes of stuff that came from ETO, it used a pair of 3CX800A7 tubes but had similar preset "bandpass tuning" caps stuffed in the RF section.  Since the bank of 8 preset T and L capacitors (again only for 4 bands) means they have to be smaller (to fit in a desktop amp), it never would have been able to reliably run 1500-plus watts.

Glenn AE0Q

This is interesting because I have a long time friend who ran an Alpha 78 for probably 25 years and just sold it recently to buy an 87A which promptly puked, and Brad to this day has never returned his calls.

Anyhow, he lacks maybe 10 DX locations working them all with it. Plus he rag chewed most every night. Big part of his life obviously.
He always drove it with 100 watts and never tuned the presets.

[AE0Q]

This is interesting because I have a long time friend who ran an Alpha 78 for probably 25 years and just sold it recently to buy an 87A which promptly puked, and Brad to this day has never returned his calls.

Why Brad?
Did your friend email me at Alpha?  I don't remember any 87A questions recently.  I check the Alpha Service email every day.
service@alpharfsystems.com

Glenn AE0Q

[KM4AH]

This is interesting because I have a long time friend who ran an Alpha 78 for probably 25 years and just sold it recently to buy an 87A which promptly puked, and Brad to this day has never returned his calls.

Why Brad?
Did your friend email me at Alpha?  I don't remember any 87A questions recently.  I check the Alpha Service email every day.
service@alpharfsystems.com

Glenn AE0Q

I did contact you. We talked about torn ACL's in dogs.  It's been a while and maybe a dozen calls to Brad while Alpha was in limbo. No response. Sorry I brought it up, was not the point.

Point was Alpha 78's not being reliable at 1500 watts out which is nonsense.

[AE0Q]

Point was Alpha 78's not being reliable at 1500 watts out which is nonsense.

Ah well, there are wattmeters, and there are wattmeters.

Having replaced too many of those tiny T and L variable capacitors in the 78 bandpass circuit, it's obvious that the power limit wasn't 1500w OUTput when the 78 was designed.  The 3 tubes are at their max Ip and the small Hipersil xfmr is, too.

[KM4AH]

Point was Alpha 78's not being reliable at 1500 watts out which is nonsense.

Ah well, there are wattmeters, and there are wattmeters.

Having replaced too many of those tiny T and L variable capacitors in the 78 bandpass circuit, it's obvious that the power limit wasn't 1500w OUTput when the 78 was designed.  The 3 tubes are at their max Ip and the small Hipersil xfmr is, too.

So, if nobody has messed with the input what will a stock Alpha 78 do with 100 watts of drive ?

If it is less than 1500 so be it, if it is 1500 or more then one has done it for countless hours and QSO's.

[VE7RF]

Here's what I want to know.  Why did Alpha switch from PIN diode TR switching in the 87A  (and manual tuned 89)
back to a vac relay in the 9500     Every xcvr uses PIN diodes for TR switching...since the 80's..with zero issues.

[W1VT]

Maybe they had trouble obtaining PIN diodes that delivered the performance they wanted at lower HF/MF?
These parts work really well at VHF and UHF but the carrier lifetimes of standard parts are often too short for excellent low frequency performance.

In the 1980s it was a challenge at time to get diodes that would work well on the 3, 5, and 10GHz bands.
Hams would use lower frequency diodes in leaded glass packages as nothing else was available.  Sort of worked at 3.5GHz.
It was a time in which a lot of parts were only available through authorized distributors.  You had to pay the overhead of having a sales representative.

[AE0Q]

Here's what I want to know.  Why did Alpha switch from PIN diode TR switching in the 87A  (and manual tuned 89) back to a vac relay in the 9500     Every xcvr uses PIN diodes for TR switching...since the 80's..with zero issues.

First, not EVERY xcvr uses them from the 80's on.  Kenwood didn't.  For the filter switching, yes, but not the T/R circuit in the 90's radios.

My guess is the high power PIN diodes cost a lot AND had/have to be special ordered in large batches from one company.  The diodes for the 87A/89 are now unavailable, although you can stuff slightly bigger ones in there.
You would have to ask Gordon W0RUN his exact reasons for the 9500 design..

[W1VT]

Mitsubishi microwave FETs had different purchasing requirement.  Instead of requiring a large order, they required monthly purchases. 
Makes a lot of sense from a cash flow perspective.  I recall buying a lot from someone who would sell them at ham microwave conferences.
He said the only way to get them was to buy them every month whether they needed them or not.

The microwave diodes I mentioned were using in diode mixers for frequency conversion.  Very basic parts.  Maybe five years after I needed them they became cheaply  available in surface mount packages.