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Author Topic: Firing up a Heath SB-1000 amp for my first time - some issues?  (Read 2999 times)
KC1GCG
Member

Posts: 123




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« on: May 22, 2017, 11:29:56 AM »

Hi all,
Finally, after weeks of getting the shack ready (dedicated power, new coax, etc) I finally got the courage to fire this baby up.
1) I am following the manual and it says on page 63 section 2 that the plate voltage on the meter should be about 3400 in the standby position. It is around 3100. Other places it says "normal" range is 2700-3500... so is this 3100 OK or a symptom?
2) Of more concern is the voltage jumps around occasionally from 3000 to 3100. Sometimes its a slow increase or decrease and other times it appears instant. Ideas or concerns?
3) On page 63 step 7 says key the exciter with zero drive and the plate current should be between 50-80ma. It is at 140 ma. I do not have a code key so I have been keying using rtty or AM. Same results.  The grid current moves to about 5ma.

Source for the amp was from a trusted friend of a friend who said when he last used it about 1 year ago all was good.

So..... I'm printing the whole manual to sit down and study and am thinking I need to treat this like a new build and go through all the alignment/testing procedures. I do not have a scope so that's why I did not do that already..... thinking that  if someone did it prior with a scope no sense undoing that. The manual does seem to have instructions for folks like me without a scope.
Thought I'd post here before diving into this in case anyone can tell me something more simple like swinging  my cat by the tail over the amp in a counter clockwise direction and all will be fine etc...

I am using it with an Icom 7300.... using the recommended relay interface between the 7300 and the amp and have the ALC connected.

Thanks fellow Ehamers. Excited about getting this sucker running finally.
Best regards
John K1JRF

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N8CBX
Member

Posts: 476




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« Reply #1 on: May 22, 2017, 12:51:06 PM »

I always verify the true plate volatge using a HV probe (Fluke).
To check the resting idle current (Checking in SSB mode only; Not AM or CW) with zero drive (no voice modulation). If a problem, troubleshoot the bias voltage regulator which is likely a 5v zener.
It sounds to me you were using AM and not SSB.
When you mentioned using an O-scope, that is for checking/verfiying the linearity (trapezoid pattern) of the amp's output to it's input. If you want to see the trapezoid pattern, a Kenwood SM-220 (Station Monitor) can do it.
Jan N8CBX
« Last Edit: May 22, 2017, 12:58:40 PM by N8CBX » Logged

Dayton Ohio - The Birthplace of Aviation
KC1GCG
Member

Posts: 123




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« Reply #2 on: May 22, 2017, 01:06:47 PM »

Thanks Jan for the reply. I'll verify that voltage with a DVM. I did see elsewhere in the manual where it says 3100 is typical so a bit of discrepancy in the manual.
I did try it in SSB mode no drive power and the plate current is still at 140ma.
Best regards
John K1JRF
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KM1H
Member

Posts: 2203




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« Reply #3 on: May 22, 2017, 01:45:58 PM »

It sounds as if the Zener may be shorted which usually happens during a tube arc.

The varying voltage could be old filter caps, tube instability, or both. Remove the plate cap and try again to test the HV, Do not key into transmit. Replacement caps are in the MFJ catalog around Pg 88 and are in all the Ameritron amps. The value is higher as cap technology advances and it improves the filtering as well as dynamic regulation of the HV which improves the IMD.

Carl
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AC2RY
Member

Posts: 205




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« Reply #4 on: May 22, 2017, 02:03:11 PM »

Hi all,
Finally, after weeks of getting the shack ready (dedicated power, new coax, etc) I finally got the courage to fire this baby up.
1) I am following the manual and it says on page 63 section 2 that the plate voltage on the meter should be about 3400 in the standby position. It is around 3100. Other places it says "normal" range is 2700-3500... so is this 3100 OK or a symptom?
2) Of more concern is the voltage jumps around occasionally from 3000 to 3100. Sometimes its a slow increase or decrease and other times it appears instant. Ideas or concerns?
3) On page 63 step 7 says key the exciter with zero drive and the plate current should be between 50-80ma. It is at 140 ma. I do not have a code key so I have been keying using rtty or AM. Same results.  The grid current moves to about 5ma.

Source for the amp was from a trusted friend of a friend who said when he last used it about 1 year ago all was good.

So..... I'm printing the whole manual to sit down and study and am thinking I need to treat this like a new build and go through all the alignment/testing procedures. I do not have a scope so that's why I did not do that already..... thinking that  if someone did it prior with a scope no sense undoing that. The manual does seem to have instructions for folks like me without a scope.
Thought I'd post here before diving into this in case anyone can tell me something more simple like swinging  my cat by the tail over the amp in a counter clockwise direction and all will be fine etc...

I am using it with an Icom 7300.... using the recommended relay interface between the 7300 and the amp and have the ALC connected.

Thanks fellow Ehamers. Excited about getting this sucker running finally.
Best regards
John K1JRF



When they say "key with zero drive" - you better use SSB with microphone disconnected. When in RTTY or AM mode - you actually apply drive of 100 or 30% respectively. What manual asks you to do - turn amp to transmit mode with no input power at all. This is to check tube bias in transmit mode. Plate voltage variation is not likely a problem - you just see line voltage variation multiplied by 30. I would check ripple to assess capacitors health, but you need high voltage probe for that.
« Last Edit: May 22, 2017, 02:07:03 PM by AC2RY » Logged
KC1GCG
Member

Posts: 123




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« Reply #5 on: May 22, 2017, 03:20:14 PM »

Thanks for the pointers so far folks.
Clarification......"When in RTTY or AM mode - you actually apply drive of 100 or 30% respectively."  When I used Rtty or AM I had the Icom 7300 RF power turned down to zero. That is ok isn't it? and not giving me as stated in quotes? Didn't say that in my first post but want to make sure that's ok going forward.
Thanks
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N8CBX
Member

Posts: 476




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« Reply #6 on: May 22, 2017, 03:22:21 PM »

...use SSB with microphone disconnected.
Well, one needs the mic connected to key it, but just turn down the mic gain will do the same thing.

I'm not familiar with the 7300, but on my TS950 there is a Carrier level control to set for AM and a Power out control on the front panel. I suggest using the power out control initially to start at low power then bring it up while doing your amp tuning and while monitoring the amp's meters & power.
Initially, you don't want to throw 100w (whatever the final drive power is) on it all at once, not until you can get beyond this amp test drive for the first time. Play it safe.
Jan N8CBX
« Last Edit: May 22, 2017, 03:37:59 PM by N8CBX » Logged

Dayton Ohio - The Birthplace of Aviation
N3QE
Member

Posts: 4756




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« Reply #7 on: May 22, 2017, 03:58:20 PM »

1) I am following the manual and it says on page 63 section 2 that the plate voltage on the meter should be about 3400 in the standby position. It is around 3100. Other places it says "normal" range is 2700-3500... so is this 3100 OK or a symptom?
2) Of more concern is the voltage jumps around occasionally from 3000 to 3100. Sometimes its a slow increase or decrease and other times it appears instant. Ideas or concerns?
3) On page 63 step 7 says key the exciter with zero drive and the plate current should be between 50-80ma. It is at 140 ma. I do not have a code key so I have been keying using rtty or AM. Same results.  The grid current moves to about 5ma.
connected.

If really at 3000VDC and 140mA idle current you should be showing substantial orange plate glow (420W dissipation).

Others point out correctly that bad grid connection or bad zener bias network could lead to this kind of idle dissipation.

If your tubes plate is not glowing orange, then your amps metering could be all messed up and the amp is actually working fine. Don't laugh but I actually grew up with hardly any metering and just judging amp performance based on plate glow!
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KC1GCG
Member

Posts: 123




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« Reply #8 on: May 22, 2017, 04:26:33 PM »

OK thanks again all.
I looked when keying... zero power out of my 7300... and all I see before keying and during is the filament. No orange or other glowing from the tube so perhaps this is pointing to messed up metering? I will go ahead and do all the checks suggested and take it slow but hopefully its just the metering.
Will check back for other ideas and will post what I find.
Regards
John K1JRF
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KC1GCG
Member

Posts: 123




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« Reply #9 on: May 22, 2017, 08:09:13 PM »

Update and more questions.....
OK checked all the diodes - all fine. No shorted caps. Coincidentally I did buy one of those multi testers - open source gadgets for caps, diodes etc this week. . Pretty cool so far to get off subject a bit... No shorted caps but can use that gadget to test them tomorrow when I have more time to pull the caps.
Looking at the manual and schematic trying to find a way to calibrate the meters all I see is one pot to just to match it to an external watt meter?? Are the plate and grid meters relying on design and components staying within spec to be calibrated? If so guess I need to check those comps too??
Also looked at some pics and vids for the filament color and it looks good and there is definitely no "other colors" from the tube.
Found more references to 3100 V on the schematic being the correct open load V so that looks good to me so far. Not sure why one spot in the manual says 3400- typo?
My DVD does not go up to 3k+ so heading out to get a new meter for the shack tomorrow.
Any other tips or pointers appreciated.
Good evening
John K1JRF
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N3QE
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Posts: 4756




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« Reply #10 on: May 23, 2017, 06:54:38 AM »

My DVD does not go up to 3k+ so heading out to get a new meter for the shack tomorrow.

No DVM goes to 3kV. You need a HV probe to get that high. But I don't think there's any problem with your HV.

And you definitely don't want to be probing around in this amp with the power on and the lid off. Follow all the safety instructions in the manual and do not defeat the interlock.

Since you seem to have some issue with plate current metering, you might try pulling the anode clip off the tube, reassemble the case, and see what the plate current reads on the amps meter when you key it. If it reads anything other than zero then there's something funny about how this box has been wired or the meter switch is all wacked out.
« Last Edit: May 23, 2017, 06:56:53 AM by N3QE » Logged
N8CBX
Member

Posts: 476




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« Reply #11 on: May 23, 2017, 08:43:49 AM »

...I need to treat this like a new build and go through all the alignment/testing procedures. I do not have a scope so that's why I did not do that already.....
I download the SB1000 manual, and they mention no "scope" usage. The alignment is for the Pi net input circuits and they say a fwd/ref power meter (SWR meter) is required to "adjust" the inductors.
Also, I don't think you understand the equipment required to measure voltage in a 3100v plate supply (as already mentioned).
I think you need to hit the books and read up some more.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
WB2WIK
Member

Posts: 21737




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« Reply #12 on: May 23, 2017, 10:47:41 AM »

Hi all,
Finally, after weeks of getting the shack ready (dedicated power, new coax, etc) I finally got the courage to fire this baby up.
1) I am following the manual and it says on page 63 section 2 that the plate voltage on the meter should be about 3400 in the standby position. It is around 3100. Other places it says "normal" range is 2700-3500... so is this 3100 OK or a symptom?
Probably okay.
Quote
2) Of more concern is the voltage jumps around occasionally from 3000 to 3100. Sometimes its a slow increase or decrease and other times it appears instant. Ideas or concerns?
Are you running the amp from a 120V or 240V line?   Either way, any small change in line voltage creates a much bigger change in HV from the power supply since at 120V the ratio between line in and HV out is about 26 to 1.    So if your 120Vac line changes by 1V, expect to see at least a 26V change in B+.   So, what you're seeing could be just line voltage fluctuations.  Might also be something else.
Quote
3) On page 63 step 7 says key the exciter with zero drive and the plate current should be between 50-80ma. It is at 140 ma. I do not have a code key so I have been keying using rtty or AM. Same results.  The grid current moves to about 5ma.
Key the amp with your rig in SSB mode and the mike gain turned down to zero.   Turning down the RF output on RTTY or AM it's unlikely the output is really ever "zero..." most rigs won't turn down to no output at all.   If your drive level really is "zero" (like SSB with mike keyed but no modulation), grid current should be zero.   Any grid current indicates something's wrong.
 
Quote
So..... I'm printing the whole manual to sit down and study and am thinking I need to treat this like a new build and go through all the alignment/testing procedures. I do not have a scope so that's why I did not do that already..... thinking that  if someone did it prior with a scope no sense undoing that. The manual does seem to have instructions for folks like me without a scope.
There's nothing to align in this amp.   I doubt Heath recommended using a scope for anything, except perhaps monitoring the output envelope under modulation to assure the amp isn't flattopping and creating distortion -- but that would be an operational observation, not any kind of test or alignment.





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K0CWO
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Posts: 468




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« Reply #13 on: May 23, 2017, 02:10:22 PM »

"If your drive level really is "zero" (like SSB with mike keyed but no modulation), grid current should be zero.   Any grid current indicates something's wrong."

I don't agree with the above statement.  The no drive keyed plate current should be 50 to 80 mA as indicated in the manual.

My AL-80A which is almost identical shows 75 mA when keyed without drive.

3100 volts is normal.

My question is: does the amplifier produce power when driven?  80 watts of drive should produce 700-800 watts of output when properly tuned.

If the amplifier shows a higher than 50-80 mA plate current when keyed, then something else is wrong as indicated in KM1H's post.
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K4RVN
Member

Posts: 2




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« Reply #14 on: May 23, 2017, 05:58:11 PM »

John your amp is almost identical to an Ameritron AL 80A which I own and have since 1989.
My advice to you is forget measuring the HV with a meter. It is very dangerous. 3100 volts is normal for that amp unloaded and will fall to about 2750 to 2800 on SSB voice input to the mike.
Connect a watt meter to the output of your amp and a dummy load if you have one and use about 20 watts drive with the 7300 in the CW or tune position. Tune the amp for max output with the load and plate controls with the 20 watts drive. Turn the 7300 to SSB. You won't hurt the amp doing this. The plate and other readings will only be a fraction of what the manual calls for when you speak into the mike. The watt meter will read when you are talking. Once you get used to tuning the amp with 20 watts drive you can increase the drive somewhat and practice some more while working up toward higher watts out. Go slow and take it easy on the old amp.
Never stick your hands in the amp while powered up to measure anything that's why they put an interlock on the top cover. There is lethal power in there.
« Last Edit: May 23, 2017, 06:00:54 PM by K4RVN » Logged
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