Ampeg PF 20t not working, halp

[BassmanPaul]

I'm guessing from your bio you're a full time technician and keen to protect your profession, which I totally understand. With that said, you should know this kind of thing comes off as condescending and makes people like me even less likely to use techs instead of self diagnosing. I'm fully aware I could spend $40-50 each way for shipping just to have a tech look at the amp, OR I could spend nothing and get great advice from people like JimmyM and Corn-on-beans. The price I pay is sorting through all the other BS



It looks like you didn't fully read or comprehend the conversation; I just asked if it should be taken apart, the answer was no, better instructions were given, I said I'd follow them. Learning was had, what's to dislike?

Regarding Andy - agedhorse. He is certainly not a technician protecting his profession. He is an EE, one of the brains who designed the Genz Benz amplifiers which he still supports. He currently works at Mesa and designed the Subway series. The fact that he comes here to offer his vast experience to help us all is a testament to his generosity.

Going inside a tube amplifier is dangerous for the neophyte. I fully comprehended the conversation. Your suggestion scared me because it shows a complete lack of knowledge and understanding of a tube amplifier.

 

[alaskaleftybass]

Can't figure out how to edit the thread title or I definitely would

Here you go-- on your first page, click on the Thread Tools button. You'll see "edit title" and there ya go...

 

[Engle]

We should have a dislike button as well as a like one. Some of the posts on this site terrify me not just for the risk to the amp but to the owner as well. Taking apart tube sockets to clean them is one such post!

I think it’s unlikely someone in the future will read only partway into this thread and remove the tube sockets from their amp to clean them.
And I don’t believe the OP would have done so, but yeah there are some alarming statements made here and elsewhere on the net.

 

[BassmanPaul]

I think it’s unlikely someone in the future will read only partway into this thread and remove the tube sockets from their amp to clean them.
And I don’t believe the OP would have done so, but yeah there are some alarming statements made here and elsewhere on the net.

I’m not so sure. I have seen worse done to a poor amplifier.

 

[Engle]

I’m not so sure. I have seen worse done to a poor amplifier.

I bet you have!

 

[agedhorse]

I'm guessing from your bio you're a full time technician and keen to protect your profession, which I totally understand. With that said, you should know this kind of thing comes off as condescending and makes people like me even less likely to use techs instead of self diagnosing. I'm fully aware I could spend $40-50 each way for shipping just to have a tech look at the amp, OR I could spend nothing and get great advice from people like JimmyM and Corn-on-beans. The price I pay is sorting through all the other BS

Actually, I'm a professional design engineer, and I am sharing the kinds of things I see regularly from folks who get into something without understanding what they are doing. It has nothing top do with protecting the service technician's profession (not mine actually), and more about getting good, factual, honest information out. When it comes to repairs, even a monkey on a typewriter can peck out a word every now and then, but wastes a lot of paper doing so.

There was nothing condescending about any of my comments, it appeared clear from your post that you were unaware of the possibility of shipping a product for repair. If that's not what you meant, your comments did not convey it.

 

[JimmyM]

I'm guessing from your bio you're a full time technician and keen to protect your profession, which I totally understand. With that said, you should know this kind of thing comes off as condescending and makes people like me even less likely to use techs instead of self diagnosing. I'm fully aware I could spend $40-50 each way for shipping just to have a tech look at the amp, OR I could spend nothing and get great advice from people like JimmyM and Corn-on-beans. The price I pay is sorting through all the other BS

Agedhorse is a highly skilled electrical engineer/amp designer, and has designed the latest bass amps from Mesa as well as many of the amps made by Genz Benz when they were on the scene. Beans is a highly skilled amp tech who's our go-to tech expert on all things Ampeg and also very knowledgeable about other amps as well. I am a bass player who knows zip about the tech end, but has learned a few things from these two gentlemen along the way about doing minor repairs.

One thing I've learned from them is their advice is right on. Andy (Agedhorse) tends to be very meticulous, always errs on the side of caution, and will tell you flat out if he thinks you're screwing up. He stands to gain nothing, as you screwing up the repair on your amp is actually better for him, as you'll need to buy another one if you do and he just happens to make a handful of very nice ones. Trust me, he's not trying to protect the tech profession at all. He's trying to protect YOU.

There are only so many things that folks like you and I can do to troubleshoot our amps. One of them happened to fix your amp. A winner is you! Take the victory, don't question it, and always remember my late dad's saying that he made up..."If it ain't broke, don't fix it."

(OK, he didn't make it up, but he told me he did and I believed him when I was 10 )

 

[BassmanPaul]

Looking into this amp more for personal interest, I was surprised that the designers went with an Octal tube, 6V6GT, to get 20W. I would have thought that a pair of EL86 tubes with fixed bias would get 20W easily. Maybe the designers just wanted to use an ‘American' tube.

Using Octals, a pair of easily obtainable 6L6GC with cathode bias would not be stressed to produce that same 20W.

 

[agedhorse]

Looking into this amp more for personal interest, I was surprised that the designers went with an Octal tube, 6V6GT, to get 20W. I would have thought that a pair of EL86 tubes with fixed bias would get 20W easily. Maybe the designers just wanted to use an ‘American' tube.

Using Octals, a pair of easily obtainable 6L6GC with cathode bias would not be stressed to produce that same 20W.

There are some "advantages" to using 6V6 family tubes, one of which is ruggedness. EL86 and EL84 tubes can get really microphonic when used as bass amp tubes. They also can sound quite different as well. The EL 86 is a lower voltage higher current version of the EL 84.

 

[Southtwin]

Hey all, for the record I very much respect and appreciate Agedhorse (Andy's) vast knowledge and experience, and looking out for people's safety. To me it was kind of like if an engineer that worked on a Cummins engine hung out on a Dodge forum and told a thrifty consumer to take it into a dealer instead of troubleshooting a fuel pump (or something). Also it's hard as hell to tell tone of voice on the internet. At the end of the day nobody got hurt and I learned a neat trick plus a thing or two about tube amp maintenance!

Here you go-- on your first page, click on the Thread Tools button. You'll see "edit title" and there ya go...

When I click "Thread Tools" the only clickable option it gives me is "Who Replied?" I'm definitely signed in, not sure why I can't find a title edit option anywhere..

 

[beans-on-toast]

Looking into this amp more for personal interest, I was surprised that the designers went with an Octal tube, 6V6GT, to get 20W. I would have thought that a pair of EL86 tubes with fixed bias would get 20W easily. Maybe the designers just wanted to use an ‘American' tube.

Using Octals, a pair of easily obtainable 6L6GC with cathode bias would not be stressed to produce that same 20W.

The 20T and the 50T were designed at the same time. Slightly different character. Two options at different prices, it helps with marketing and sales.

The 20T was a take on the Ampeg SB-12, an 18W bass amp. The SB-12 started out with a pair of 7868 power tubes but later revisions used the 6L6GC. Using the 6V6GC allowed them to present two amps that didn’t appear to be much the same that only differed in wattage.

Ampeg had a similar guitar amp based on the 6V6GT called the Rocket. It had a 5Y3 rectifier. The Rocket was Ampeg’s take on the Fender Deluxe. There’s heritage in the 6V6 that people like. BTW, both had mods to use 6L6GC tube to change the headroom a bit.




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[BassmanPaul]

There are some "advantages" to using 6V6 family tubes, one of which is ruggedness. EL86 and EL84 tubes can get really microphonic when used as bass amp tubes. They also can sound quite different as well. The EL 86 is a lower voltage higher current version of the EL 84.

To be honest I meant EL84 - memory played tricks on me again. I have always found the EL84 a very rugged tube. It's used in what can be classed as one of the best guitar amps ever built the top boost VOX AC30. Those amps just kept going and going.

I last used a 6V6GT when I built a record player amp in my early teens. It worked too! My dad was very surprised!

 

[agedhorse]

The EL-84 tube as a family can be very mechanically noisy and microphonic. It's the most problematic tube I have worked with in this regard.

 

[BassmanPaul]

The EL-84 tube as a family can be very mechanically noisy and microphonic. It's the most problematic tube I have worked with in this regard.

Interesting - thank you for your insight!

 

[Alper Yilmaz]

@agedhorse

Hey Andy,

Sorry to dilute to topic a bit, but do you happen to have any experience with SV83’s? Do they have similar issues like the EL84’s? I understand that SV83’s are video tubes; correct me if I am wrong. I have a home stereo amp by Decware which can use both SV83 and EL84 output tubes, but the sound that comes from the SV83’s is really to die for. I am not sure if they are swappable in all applications, but they are on my Decware. Of course, bass amplification in contrast to home stereo applications can be quite different...

Best,

Alper

The EL-84 tube as a family can be very mechanically noisy and microphonic. It's the most problematic tube I have worked with in this regard.

 

[agedhorse]

@agedhorse

Hey Andy,

Sorry to dilute to topic a bit, but do you happen to have any experience with SV83’s? Do they have similar issues like the EL84’s? I understand that SV83’s are video tubes; correct me if I am wrong. I have a home stereo amp by Decware which can use both SV83 and EL84 output tubes, but the sound that comes from the SV83’s is really to die for. I am not sure if they are swappable in all applications, but they are on my Decware. Of course, bass amplification in contrast to home stereo applications can be quite different...

Best,

Alper

I have no experience with that tube, sorry

 

[Southtwin]

Belated update, but the previous "fix" was short lived unfortunately. Reseating the tubes caused the amp to work again for a week or so, but then went back to previous state (powers up, red led comes on, but won't exit standby and no sound passes). I got the deoxit d5 and microbrushes and scrubbed the pins and sockets, no change. I'll probably buy a couple of replacement 6v6 power tubes just to see if changing those fixes it (my only other tube amp is a 90s Fender Twin with 6L6B power tubes and I'm guessing it'd be bad to swap those in for the Ampeg's 6v6s to check functionality); I have a couple of other random 12ax7s to check preamp tubes with, I'm assuming it's fine to use non-matched pair as long as they're 12ax7s.

If that doesn't fix the problem, I'm ready to send it to a tech. The Ampeg site lists several but I'm having trouble contacting the ones within a 2-4 hour drive of me, seems they're out due to covid. Would anyone reading this be willing to work on it for a reasonable rate or recommend someone?

 

[AudioTaper]

Belated update, but the previous "fix" was short lived unfortunately. Reseating the tubes caused the amp to work again for a week or so, but then went back to previous state (powers up, red led comes on, but won't exit standby and no sound passes). I got the deoxit d5 and microbrushes and scrubbed the pins and sockets, no change. I'll probably buy a couple of replacement 6v6 power tubes just to see if changing those fixes it (my only other tube amp is a 90s Fender Twin with 6L6B power tubes and I'm guessing it'd be bad to swap those in for the Ampeg's 6v6s to check functionality); I have a couple of other random 12ax7s to check preamp tubes with, I'm assuming it's fine to use non-matched pair as long as they're 12ax7s.

If that doesn't fix the problem, I'm ready to send it to a tech. The Ampeg site lists several but I'm having trouble contacting the ones within a 2-4 hour drive of me, seems they're out due to covid. Would anyone reading this be willing to work on it for a reasonable rate or recommend someone?

That stinks.
I would be careful of 'anyone' willing to take a look at it.

I was thinking of this the other day; with a good portion of the country shut down, where are items being repaired?

 

[agedhorse]

I would suggest stopping at this point, NOT replacing the power tubes and let a QUALIFIED tech continue on with troubleshooting, diagnosing and repairing. That way, you have a warranty on the tubes and somebody who will (or should) stand behind their repair. Most techs will not warranty tubes that they do not install.

 

[Southtwin]

I would suggest stopping at this point, NOT replacing the power tubes and let a QUALIFIED tech continue on with troubleshooting, diagnosing and repairing. That way, you have a warranty on the tubes and somebody who will (or should) stand behind their repair. Most techs will not warranty tubes that they do not install.

Can you suggest anyone, preferably in eastern US?