amp pop question

[madbean]

In the last few days my Champ has emitted a few pops when warming up after turn on. Audio output comes on suddenly after two or three pops rather than the normal fade in to full volume.

I'm thinking maybe the 6V6? It was last replaced in 2017 and I used a 6v6S from JJ. All the tubes look to be glowing normally and I swapped out the 12ax7 JIC (no difference). Do you think this is a good guess or should I also replace the rectifier tube? The amp had a full service in 2015 or 2016 IIRC so I'd be surprised if it's a component failure. But, maybe I better take a look inside anyway.

[cooder]

I would guess checking the output and rectifier tube first would be the easiest to eliminate that as a cause, if you have spares handy.
Could also be a wee bit of arcing on tube sockets maybe, so if you don't have spare tubes to check I would take the tubes out and back in again, maybe a bit of contact cleaner on sockets and give them a bit of a wiggle when putting back in.

[cooder]

If the tubes and sockets aren't the culprits, then the next thought would be checking the filter caps. If it has the Fender typical IC caps they are a bit notorious for not holding out well and the insulation might be breaking down inside., or even visibly leaking. F&T caps for the win would be an upgrade anyway.

[Aentons]

maybe a bit of contact cleaner on sockets and give them a bit of a wiggle when putting back in.

I had something very similar happening with my AC30 for a bit. Deoxit in the sockets and wiggle took care of it

[Zigcat]

Deoxit can be conductive, so clean the sockets with isopropyl afterward to get all of the deoxit cleaned off.

[Aentons]

Deoxit can be conductive, so clean the sockets with isopropyl afterward to get all of the deoxit cleaned off.

http://store.caig.com/s.nl/ctype.KB/it.I/id.703/KB.215/.f#:~:text=DeoxIT%C2%AE%2C%20DeoxIT%C2%AE%20GOLD,or%20any%20other%20conductive%20constituents.

D5 is flammable... but not conductive

[gordo]

Didn't you have this serviced a while back?

[fair.child]

Check your B+ whether it's still within voltage range. If not, then cooder suggestion is correct. Replace the filter caps. Power Tubes like 6V6 may be the issue but it won't be the first place I look to debug. I will generally go check the Output transformer primary voltages and B+ to start to determine whether the filter caps need to be replaced

[thesmokingman]

you don't have a lot of tubes to check and if your troubleshooting goes beyond that then it is time to chopstick ... tapping on the caps and resistors will cause those that are breaking down to be rather microphonic

[madbean]

Had some time this morning to take a look inside. All the filter and bypass caps were replaced as I thought. Those are only a few years old at this point and all seemed to be in good condition. For the filter caps they used one can cap w/two 50uF/500v. The third filter cap is an F&T 2u2/500v (the one right before the two 100k plate resistors) so it's been modded. I also remember them recommending dropping the B+ voltage slightly from spec (maybe to give the power tube a longer life? I don't remember).

Anyway, I cleaned all the tube pins and sockets but no dice. Still popping twice on power up. I'm going to take some voltage readings to see what I find. In the meantime, CEDist actually had some JJ 6v6 and 5y3 at really good prices so I'm ordering those as replacements or at least backups. It looks like the 5y3 is original, or at least very not new. At some point, I want to find some mojo tubes for this amp but right now it just needs to work.

[Aentons]

That blue 470ohm resistor looks crispy

[Aentons]

Uncle Doug and Psionic (Lyle Caldwell) are a wealth of info on amp repair. Including lots of talk about common issues and fixes for fender stuff

Maybe not these particular videos, but I would search their channels for any vids that maybe look related
https://youtu.be/zm8_I2NthDM

https://youtu.be/XH4FD1PuNvs

[Zigcat]

You have 100uf on the first b+ node!? You 5y3 might be arching in a painful death. Way too much filtering for a tube rectifier.

Edit: Looks like it might be 50uf on the first node. Still too much for that rectifier. My guess is that that 5y3 is the culprit.

[madbean]

That blue 470ohm resistor looks crispy

Yeah I noticed that as well. No smell from it but it could be easily replaced.

[cooder]

You have 100uf on the first b+ node!? You 5y3 might be arching in a painful death. Way too much filtering for a tube rectifier.

Edit: Looks like it might be 50uf on the first node. Still too much for that rectifier. My guess is that that 5y3 is the culprit.

This.^
If you have 50 uF on first node you could try a GZ34 rectifier, but that will also increase the B+ voltage a bit.
GZ34 are rated for max 60uF on first node, so that should be good. An advantage of the GZ34 is that it is indirectly heated an that means a nice gentle slow start up of hi voltage (about 12 to 15 sec).