Ampeg PF 20t not working, halp

[Wisebass]

hi Southtwin

pulled and reseated all the tubes, working like a charm now (LED does switch to purple when working properly btw)

Lucky guy! Great to see that it was such an easy fix and your amp works again.

Any electronics store nearby can fix it for real cheap. Probably just fried a transistor or something.

I would not take my amp to someone who looks for transistors in an all tube amp!


greetings

Wise(b)ass

 

[JimmyM]

I'm really surprised at your response Andy!
You've been here long enough to know that nearly every tube amp problem is related to a tube or a fuse; major tube amp users on this board suggest this on nearly every thread.

Then again, they are the same ones that are quick to mention that tubes last a very long time, which has been my experience for 40 years. And when the do fail on their own, it is almost always a slow process. Thankfully the usually only die like a light bulb when another component fails.

Sorry Jim...not seeing the disconnect. I've seen some tubes die quickly because of a bum tube and no other reason. Used to be pretty common with the new Russian/Chinese tubes out there.

I don't have the schematic for this amp but am curious.
How could a bad tube could keep the amp from coming out of standby?
Especially since the OP stated that the tubes aren't seeing any voltage (by not heating up).

In this case, it was because one of them wasn't making a good connection in the socket.

 

[alaskaleftybass]

It's scary to think that a loose tube could kill my money making amp. (I do have a backup amp too). If the OP were to drag that amp all over for playing small gigs what are the chances of it losing connection again? I'm just thinking out loud because I've been considering one of those PF-20T's.

 

[SirMjac28]

Glad you got it working now the info is available for everyone

 

[JimmyM]

It's scary to think that a loose tube could kill my money making amp. (I do have a backup amp too). If the OP were to drag that amp all over for playing small gigs what are the chances of it losing connection again? I'm just thinking out loud because I've been considering one of those PF-20T's.

Pretty low unless he drops it.

 

[Southtwin]

The only issue still in my mind is why the hell did this happen in the first place? I haven't been gigging at all, just working on new material by myself (i.e. amp hasn't been moved in months). I love the sound of the PF-20t and haven't heard of any other reliability issues, but it seems weird that electrons suddenly wouldn't be flowing well through newish tubes (JJ 6v6s, Ruby 12ax7s) that were well-seated and secured

 

[jnewmark]

If I had the cash or lived anywhere near qualified techs I wouldn't be posting on here, no offense but I'd really appreciate it if people only post if there's something useful/productive to add

Should be a sticky at the top of this Forum.

 

[beans-on-toast]

The only issue still in my mind is why the hell did this happen in the first place? I haven't been gigging at all, just working on new material by myself (i.e. amp hasn't been moved in months). I love the sound of the PF-20t and haven't heard of any other reliability issues, but it seems weird that electrons suddenly wouldn't be flowing well through newish tubes (JJ 6v6s, Ruby 12ax7s) that were well-seated and secured

Good to see that you sorted it. The amp is well made and has reliable single board construction.

I am concerned that both the preamp out AND the power amp were affected. A tech would open the amp and inspect and re-seat the connectors, pay particular attention to the power supply ones. Moving the amp to work on it might have have caused something to shift and make it work. It could be temporary so it should be checked.

Oxidation, both on tube pins and socket contacts can be a problem with even new amps. Reseating can partially clean a contact enough to get it going again. It would be a good idea to follow up by carefully scrubbing the tube pins and socket contacts with deoxit D5 and a plastic interdental brush (available at a pharmacy).

If a tube shield is not on straight, it can cause a tube to sit askew and stress the socket contact. Ensure that the spring at the top of a shield is pushed in all the way and sitting square in the shield.

What could have caused this? Heating and cooling cycles, seasonal changes, and various electrical contacts that needed reseating could have contributed. We’ll never know for sure.

 

[agedhorse]

1. Do not spray DeOxit anywhere in the amp.

2. Do not damage the sockets by forcing anything into the pin receptacles.

3. Be darn sure there's no voltage present.

 

[Southtwin]

It would be a good idea to follow up by carefully scrubbing the tube pins and socket contacts with deoxit D5 and a plastic interdental brush (available at a pharmacy).

Great, that's super helpful. Quick question, can I directly spray Deoxit D5 directly into the socket contact without removing them from the amp and then clean with interdental brushes, i.e. is it fine for the Deoxit to run down into the amp? Also I'm assuming "micro tight" like these on Amazon would be the best size

Also just saw Agedhorse's response.. does this mean the sockets should be removed from amp and taken apart to be cleaned? If so is this commonly done on newer tube amps? Sounds like more aggravation than I'll probably get into considering I'll probably get a higher wattage SS gigging amp anyway and keep this for recording/writing at home..

 

[beans-on-toast]

Great, that's super helpful. Quick question, can I directly spray Deoxit D5 directly into the socket contact without removing them from the amp and then clean with interdental brushes, i.e. is it fine for the Deoxit to run down into the amp? Also I'm assuming "micro tight" like these on Amazon would be the best size

Also just saw Agedhorse's response.. does this mean the sockets should be removed from amp and taken apart to be cleaned? If so is this commonly done on newer tube amps? Sounds like more aggravation than I'll probably get into considering I'll probably get a higher wattage SS gigging amp anyway and keep this for recording/writing at home..

You only need the smallest amount of deoxit D5. Spray the deoxit onto the brush (yes, the one in the link looks fine), then carefully scrub the contact. Use a small lid or container to spray into. I use a clean glass spice bottle to give you an idea. When scrubbing the contact, do not use a lot of force so as to bend the metal contact open. A newish amp should not require a lot of scrubbing. Don’t forget to do the tube pins as well.

DO NOT let it drip into the amp or go anywhere but on the intended metal contact. Clean it with a Q-tip or cotton makeup pad if this happens.

Do not spray onto the tube socket. You don’t want it on the socket’s insulator material.

Do not remove the tube socket. Never never.

It really isn’t a lot of aggravation to take care of the amp, it’ll not take a lot of time. For some reason, I find that some amps that are manufactured in China require this cleaning/socket reseating. The packaging should prevent issues but the ocean crossing in a can take a toll. The need to clean and reseat with new products comes up time and time again.

By the way, all amps need some maintenance, even solid state ones.

Heed the comment above about making sure that the amp is discharged before working on it.

 

[Southtwin]

10-4, will follow all that to a T. I don't mind a bit doing moderate maintenance; I'm happy to change my oil, fuel, and air filters but I'd rather not change a head gasket or mess with a transmission. This was made in China and the shipping conditions comment makes sense to me

 

[JoeWPgh]

I would keep a close eye on it and an eye out for a qualified tech. The unknown is whether reseating the tubes fixed the problem, or if the act of doing do jostled a dicey connection in the amp. It's odd that all of the tubes went out.

 

[Southtwin]

I think I paid $400 for it used, I have to assume any tech bill for actual repair work would be around $300 so it's a bit tough to justify paying that vs selling for parts and buying another if it really was non-functional. Also I live in Jenkins KY, 2.5 hrs to Asheville NC, 4 hrs to Cincinnati, 5 hrs to Nashville (nearest places that might have techs) and it'd have to be a super expensive one-of-a-kind amp for me to justify driving that far or paying shipping costs

 

[agedhorse]

Great, that's super helpful. Quick question, can I directly spray Deoxit D5 directly into the socket contact without removing them from the amp and then clean with interdental brushes, i.e. is it fine for the Deoxit to run down into the amp?

Good God, no!!!

I think I paid $400 for it used, I have to assume any tech bill for actual repair work would be around $300 so it's a bit tough to justify paying that vs selling for parts and buying another if it really was non-functional. Also I live in Jenkins KY, 2.5 hrs to Asheville NC, 4 hrs to Cincinnati, 5 hrs to Nashville (nearest places that might have techs) and it'd have to be a super expensive one-of-a-kind amp for me to justify driving that far or paying shipping costs

It depends on the problem, your assumption of $300 for a repair is incorrect. A QUALIFIED, PROFESSIONAL service tech will diagnose the actual problem and then repair what's actually wrong. If it's something fairly minor, the cost should be reasonable provided you (or somebody else) hasn't messed other things up.

Regarding location of service depots, we have a thing in this country called a shipping industry which allow you to ship things to places that aren't local to you. Provided you package your amp up securely and well protected, this is a viable way of handling your issue. Be sure that the service shop is both professional and qualified, as well as having a verifiable track record of customer service.

 

[BassmanPaul]

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!

 

[alaskaleftybass]

Hey all, I am by no means an amp/electronics guru, but I know enough to isolate issues and occasionally solder. My beloved Ampeg PF-20t recently quit working and I don't know why. I generally run it at very low volume (gain cranked, volume at 1, Caline 10 band eq pedal with gain all the way down) so as to get rich creamy distortion without pissing off nearby neighbors. The last time it was working, I accidentally left the amp on (not standby) for a few hours with instrument volume down before going back to practice room and turning it off.

Ever since, it's had the following status: power switch works (I hear slight normal electrical hum in amp), the red LED in front comes on, but no change when I flip standby switch. No output to speaker cab (verified cab is fine), no signal from DI out (preamp or power amp), none of the tubes glow at all, and LED color doesn't change (I think it's supposed to switch to blue when not on standby, I covered LED with tape long ago and don't remember for sure). Had a ceramic fuse so I can't tell if that's the issue, just ordered glass replacement fuses but I'm assuming it wouldn't come on at all if fuse was blown. I don't currently have a multimeter or tube tester but might be willing to buy if need be. Tried searching the forums but no luck. Any help for next steps or possible culprits is appreciated!

@Southtwin I'm glad you got the situation taken care of. Now I'll tell you what a moderator told me on one of my posts. "If you got the issue fixed, notate in the title 'Resolved' so users will know in advance." Once again, congrats.

 

[Southtwin]

Regarding location of service depots, we have a thing in this country called a shipping industry which allow you to ship things to places that aren't local to you. Provided you package your amp up securely and well protected, this is a viable way of handling your issue. Be sure that the service shop is both professional and qualified, as well as having a verifiable track record of customer service.

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

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!

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?

 

[Southtwin]

@Southtwin I'm glad you got the situation taken care of. Now I'll tell you what a moderator told me on one of my posts. "If you got the issue fixed, notate in the title 'Resolved' so users will know in advance." Once again, congrats.

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

 

[BOOG]

Here's a free pamphlet to get you started: http://www.tubebooks.org/Books/army_theory.pdf

There’s a worm hole I don’t want any part of