2204 build thread

[Pete Farrington]

Windsor was blowing mains fuse prior to this build, and was popping/crackling violently. PT would get pretty hot too. If you don’t think this is enough to warrant a damaged PT, then I guess i’ll leave it in

It's not doing that now though, is it?
If not, I think we can assume the issue was related to the circuit, rather than being a faulty PT.

Video of hiss/popping. It is dead quiet when I pull V1

Maybe the valve in V1, or its anode load resistors, are noisy?
Or the silver mica caps breaking down, modern production has a bad rep.

 

[JM5010]

It's not doing that now though, is it?
If not, I think we can assume the issue was related to the circuit, rather than being a faulty PT.


Maybe the valve in V1, or its anode load resistors, are noisy?
Or the silver mica caps breaking down, modern production has a bad rep.

I may leave this as-is. I replaced the 220k plate resistor on v1a and it helped a bit actually. Just won’t play it too loud because the hissing is awful.

 

[Pete Farrington]

Make sure to use a MF type resistors, for the input stage circuit at least. Preferably 1W at the grid and the anode.

 

[JM5010]

All done!

 

[Trouble]

Having the amp open on the bench can produce noise that might go away when the head is in the cab with shielding tape.

 

[JM5010]

Oh shit, it blew the HT fuse! This happened with the Winged C EL34’s.
The 2204 fuse is T500mA 250V, while the one in the Peavey circuit is T1.5a.

Edit: Used the T1.5a HT fuse from the peavey. All seems good, however i suspect these Winged C’s are going bad, as one of these fell on the floor a few months back. There is some white dust in this tube.

 

[XTRXTR]

White dust/ powder means loss of vacuum - tube is unusable, will cause a current overload condition and cause the HT fuse to blow. Also keep the HT fuse 500mA...its a 50 watt amp now, can also damage OT primary if fused high.

 

[JM5010]

White dust/ powder means loss of vacuum - tube is unusable, will cause a current overload condition and cause the HT fuse to blow. Also keep the HT fuse 500mA...its a 50 watt amp now, can also damage OT primary if fused high.

Gotcha, will order spare fuses and some fresh power tubes. I'm thinking EH or JJ, as well as a low noise tube in V1.

 

[XTRXTR]

The dropping resistors are Metal Oxide at least 2 watt? I noticed the preamp knob as you turned it started the crackle but it continued after and when the MV is turned no change. The preamp V1a circuit is receiving crackling signal from somewhere even when the jack has nothing plugged in. Normally ground would kill signal fed into the circuit from the closed jack. Does it crackle with a guitar plugged in? chop stick and hit all dropping resistors, the Load resistors for V1 the cathode resistors for V1, bypass cap for V1, coupling caps between V1b and V1a. Are the 1MA pots new? Maybe try a new pot anyway. Interesting problem. Also test all resistance values for dropping and the V1 load and cathode. is V1 B+ steady VDC on the meter? look for cold solder joints too.

Video of hiss/popping. It is dead quiet when I pull V1. Amp is still cold biased also.

V1: JJ ECC83S
V2: GT 12AX7
V3: JJ ECC83S
V4-V5: Ruby EL34

 

[JM5010]

The dropping resistors are Metal Oxide at least 2 watt? I noticed the preamp knob as you turned it started the crackle but it continued after and when the MV is turned no change. The preamp V1a circuit is receiving crackling signal from somewhere even when the jack has nothing plugged in. Normally ground would kill signal fed into the circuit from the closed jack. Does it crackle with a guitar plugged in? chop stick and hit all dropping resistors, the Load resistors for V1 the cathode resistors for V1, bypass cap for V1, coupling caps between V1b and V1a. Are the 1MA pots new? Maybe try a new pot anyway. Interesting problem. Also test all resistance values for dropping and the V1 load and cathode. is V1 B+ steady VDC on the meter? look for cold solder joints too.

Dropping resistors are 2W 10K metal oxide. All the pots are brand new besides the treble pot.
I did chopstick around to see if anything affected this issue, had no luck though. Perhaps the wire feeding B+ to V1 isn't in the best position...I even used shielded cable on the gain pot and input jack to see if it would help.

 

[JM5010]

If this is useful, I measured my wall voltage at around 126.8v AC. From my understanding, this should be raising voltages a bit throughout the amp.

 

[Pete Farrington]

Perhaps the wire feeding B+ to V1 isn't in the best position...

That node should be very clean, no signal or HT ripple, pretty much equivalent to 0V common.

 

[XTRXTR]

I would invest into an Oscope, something working, old and cheap, used, around 25MHz max if you can find one. Otherwise the cheapest you can find. Or take this to a tech you can trust. I'm not sure you can find the issue without a scope or replacing the most obvious logical to the least logical component at fault.

Clearly if removing V1 stops the crackling then the PT is not of any concern here so don't go down that road. I say that because if it were you would still hear noises from the rest of the circuit and MV would affect it. Has to be isolated to anything connected to V1. It is possible that V1 itself could be doing that, I've never heard that noise from a microphonic tube but it is possible. I know you said you ordered one. The input jacks are new?

If treble pot was doing it you would hear it with MV up and dialing treble pot even with V1 removed.

If V1 was a tube you used from the Windsor... that is the most logical thing right now. The V1 socket is new?

Anyway I feel your pain dude. The solution will reveal itself.

 

[JM5010]

I would invest into an Oscope, something working, old and cheap, used, around 25MHz max if you can find one. Otherwise the cheapest you can find. Or take this to a tech you can trust. I'm not sure you can find the issue without a scope or replacing the most obvious logical to the least logical component at fault.

Clearly if removing V1 stops the crackling then the PT is not of any concern here so don't go down that road. I say that because if it were you would still hear noises from the rest of the circuit and MV would affect it. Has to be isolated to anything connected to V1. It is possible that V1 itself could be doing that, I've never heard that noise from a microphonic tube but it is possible. I know you said you ordered one. The input jacks are new?

If treble pot was doing it you would hear it with MV up and dialing treble pot even with V1 removed.

If V1 was a tube you used from the Windsor... that is the most logical thing right now. The V1 socket is new?

Anyway I feel your pain dude. The solution will reveal itself.

All sockets are new, got them with the Mojotone kit. They are Belton sockets

 

[JM5010]

Uh oh...MV can’t go over 2 or else this happens

 

[XTRXTR]

• Is V1 replaced?
• Did this happen with the Windsor?
• What are the output tubes biased at, grid, plate, screen, and cathode values, type?

 

[JM5010]

• Is V1 replaced?
• Did this happen with the Windsor?
• What are the output tubes biased at, grid, plate, screen, and cathode values, type?

Yep V1 is replaced with a JJ ECC83S.
Output tubes are biased at -38.5V, plate voltage is 455V. All typical marshall values for the components you mentioned. I took the chassis out and it seems to not kill itself while playing it like that. Probably a cold solder joint somewhere

No, this did not happen with the windsor

 

[Pete Farrington]

Output tubes are biased at -38.5V, plate voltage is 455V

The anode or cathode idle current which results from those electrode voltages is very beneficial to know.
As for a given set of screen grid and anode voltages and anode current, bias voltage may vary +/-25%.

 

[JM5010]

The anode or cathode idle current which results from those electrode voltages is very beneficial to know.
As for a given set of screen grid and anode voltages and anode current, bias voltage may vary +/-25%.

Which pins do i measure? I’m assuming pins 1 & 8?

 

[JM5010]

Crackling issue is gone, turned out to be a cold solder joint on the first coupling cap on V1