Ampeg VT22/V4

[lowell]

I just finished recapping and retubing the entire amp. Also cleaned all sockets and switches etc...

I realize all standby switches can tend to pop. But this is really bad... when flipped INTO standby (B+ disconnected). I replaced the switch and still the same result.

Any suggestions?

There is a lot of hum as well and I'm troubleshooting that now. Otherwise the amp is working.

http://www.ampegv4.com/images/VT22_Schem2.jpg

[lowell]

Sorry wrong schematic http://www.ampegv4.com/images/schematics/V4.jpg

[TigerAmps]

Question:

a) Did you re-locate any of the capacitor grounds or did all the grounds remain connected to the original locations?

b) Did you check the bias current. These are non-adjustable and depending on the tubes, you might need to change the bias voltage.
If they are drawing too much current at idle, it will result in a hum as well. If they draw too much current, it will both hum and red plate!
You can change the bias resistors a little to increase the bias voltage and lower the current draw thru the power tubes.

[olddawg]

I owned/used a VT 22 decades ago. There are 2 things I remember about the amp. 1) It weighed as much as a small car and 2) The standby popped like a bitch. I always just assumed it was transition arc in the switch.. but you said you replaced the switch. Btw.. if the rocker switches ever go bad.. good luck finding replacements. Great sounding amp at a rediculous volume.

[lowell]

Olddawg. Agreed!! It's gotta be 170lbs or close!!! Has 2 Altec Lansing speakers too and they're super heavy.

TigerAmps. After figuring I had the wrong schematic (I'm an idiot) I regrounded a couple caps appropriately and it reduced the pop to an acceptable level IMO.

Now. The bias is cold at 22ma per tube. So it's not a bias issue. It is affected by the tone controls so it's in the preamp. Maybe I messed up another ground. I'll keep searching. The hum balance works, and is not the cause.

[TigerAmps]

OK other thoughts:

a) I would then check the input jack grounds (remove the nuts and clean both sides of the chassis and re-tighten.)
b) Check the solder joints going to the controls (wires and pots). This is often an issue with the B25's I have seen.
Also, are the wires solid or braided? I once saw a solid core wire running to one of the switches was cracking or cracked.
It looked good, but was making a poor connection at the switch.
c) Check the solder joint of the pots on the control panel board
d) Check the input jack ground where it is soldered to the main circuit board.

I know - the control board is somewhat of a pain to remove, but worth checking anyway.

[g1]

Wiggle all the pre tubes around in their sockets to expose any oxidized sockets or socket solder issues.
Also check that the input jacks and volume pots are clean and jacks are shorting and vol. are going to zero. Mine hums a lot if I forget to turn down the channel I'm not using.

[Enzo]

You may have biased the thing properly, but what does the bias do in standby? Doesn't it go away? meaning the tube bias changes when you flip the switch?


In my mind - and this is just an opinion - no one flips that switch while playing, so having it pop is not really a problem. I consider it cosmetic.

[lowell]

Thanks. Ended up being the cap grounds. The 6K11 filter was shared in a X2 cap can. Separated them and grounded 6K11 with preamp filters. Other was B and goes to rectifier ground. Pretty quiet now.... still some hum but seems acceptable.