2204 Build with Marstran OT

[neikeel]

I like Lemco and RS micas. You can still get them around 270 and 500pF easily

 

[playloud]

I like Lemco and RS micas. You can still get them around 270 and 500pF easily

I got some of these for my build (nominally 510pf, but the actual testing values for the 4 caps were 496, 497, 502 and 503pf - 5% tolerance works to your advantage here!)

560pf is also easy to find. Less so the 556pf, but similar logic applies.

 

[Chris-in-LA]

Quick question. I’m trying this setup for the grounding buss as many of you don’t like soldering the buss to the back of the pots. Does that cap on the presence pot look to be soldered on ok? It’s supposed to be soldered to the buss and that lug.

Also, I grounded the buss to one of the power tube lugs per a suggestion from @neikeel

 

[Spanngitter]

I would GND the Power Tubes at the first Filter Cap node and not carry the bus to the signal side.
Also keep the Presence and Master GND separate from the PreAmp GND to calm the Amp a bit more down...
Lyle Caldwell (Psionic Audio) has a nice video on utube on 2204 GND improvements, maybe give it a shot.

 

[neikeel]

Yep I run the presence pot ground to the PI filter cap ground.
I end the preamp bus before the bass pot. The bias caps only get grounded at the output tube ground points.

 

[Chris-in-LA]

Yep I run the presence pot ground to the PI filter cap ground.
I end the preamp bus before the bass pot. The bias caps only get grounded at the output tube ground points.

What do you ground the preamp buss to?

 

[Spanngitter]

What do you ground the preamp buss to?

usually with the preamp cathodes and the B3 Filter Cap

 

[Chris-in-LA]

Looks like I’m ready to begin soldering all the flying leads. I had to order a few more 1 watt 100k plate resistors for V1 and v2 as I did not receive enough of them from Valvestorm. I did put in a few 1/2 watt resistors but they didn’t look right compared to all the 1 watt resistors already on the board.

 

[Gene Ballzz]

Looks like I’m ready to begin soldering all the flying leads. I had to order a few more 1 watt 100k plate resistors for V1 and v2 as I did not receive enough of them from Valvestorm. I did put in a few 1/2 watt resistors but they didn’t look right compared to all the 1 watt resistors already on the board.

View attachment 101005

Looking good! I'm at just about the same point on my long sitting TWI-LUXE build!
Best To Ya My Friend!
Gene

 

[Chris-in-LA]

Finished wiring the high voltage and power tube sockets.



I know that the grounding looks a little funny but I plan to revisit that if I have any problems with hums or buzzing. But, for now, the pots are wired in.

 

[Chris-in-LA]

Just about done. Only need to add the power cord and then I can start testing.

 

[playloud]

Looks great! Fingers crossed

 

[Chris-in-LA]

So I fired up the amp on the light bulb limiter and everything looked good. I had high voltage everywhere it was supposed to be, the heaters all read 3.15. I had -45v to the control grids. But things changed after I put in the power tubes. I had about 450v at the plates The -45v dropped to about -3v and I could barely get a reading in Mv at the 1ohm resistor on pins 1 and 8.

I decided to put in the preamp tubes and check again. No change except that I got loud static through my bench speaker when trying to read the -v to the grid. At that point I started to hear a rhythmic squeak through the speaker with the volume at zero. Probably an oscillation, might need to reverse the wires to the plates. But, first I plan to try a known good set of working power tubes tomorrow after sleeping on this problem.

Any suggestions?

 

[Chris-in-LA]

The back panel says to use a 2A fuse on the mains. The Metro list on Valvestorm says to order a 3A fast blo, of which I have several. But I thought that a 2A slo-blo was used for the mains.

 

[neikeel]

In the US @ 120v I think T3A (SLO-BLO) is what you want for mains on a 50w. HT is always the same at 500mA.

 

[Pete Farrington]

But things changed after I put in the power tubes. I had about 450v at the plates The -45v dropped to about -3v and I could barely get a reading in Mv at the 1ohm resistor on pins 1 and 8

Are you sure the wiring to the sockets is going to the correct pins?

 

[Chris-in-LA]

Are you sure the wiring to the sockets is going to the correct pins?

Yes. I’ll double check tonight. 1, 2, 7 and 8 for sure. 3 is plates, 4, 5 and 6 looked fine and voltages seemed right until I put in the power tubes. Should the power tube voltages look normal even without the preamp tubes in? Specifically, I am asking if I should be able to read or set the bias even without the preamp tubes in, correct?

 

[Chris-in-LA]

Are you sure the wiring to the sockets is going to the correct pins?

Something funny with the power tubes. V4 P1 = 4mv, V5 P1 = -450mv. Everything is wired correctly, getting ready to put in a different pair of tubes. It did look like I had the wires to the plates (p3) reversed per the diagram so I switched those before these measurements.

 

[Chris-in-LA]

Not the tubes. Need to check the 1ohm resistors.

 

[Chris-in-LA]

The problem was that one of the one ohm resistors was not completely soldered in place. However, the highest reading I can get at the bias is 13 mV. It looks like I might have to change out a resistor in the bias circuit but I’m going to do some more testing first.