Is this possible?

[Pochie45566]

Friend and I were messing around with his silver tone 1472 old beat up amp and decided to build a marshall 2204 tonestack into the amp. As marked we cut out the tone knob of the silver tone and used the gap made to install a full marshall 2204 tonestack. The mod is done and the EQ works, however i have very little gain. Im pretty stupid when it comes to all of this (all safety procedures followed) but I have included diagrams of where i cut and installed. Any help is awesome!

PS. the red x's on the diagrams are where I cut the marshall tonestack into the amp.

[brewdude]

If I understand correctly, you simply put the Marshall stack in where the old stack was?  Without changing anything else?


The Marshall has 2 gain stages and a cathode follower to drive the "lossy" tone stack.  The Silvertone has only one gain stage before the stack and no CF.

[Pochie45566]

If I understand correctly, you simply put the Marshall stack in where the old stack was?  Without changing anything else?


The Marshall has 2 gain stages and a cathode follower to drive the "lossy" tone stack.  The Silvertone has only one gain stage before the stack and no CF.

Yeah thats what I was thinking... lol i figured the loss of drive was because I was losing any output I had out of v1 to drive v2.. How to make it less "lossy"? Could I not add that 6au6 perhaps after v1

After all this amplifier is obviously much less powerful amp than a 40w 2204. We are simply looking to "hot rod" it and it had a very unpleasant eq when it was driven so I quickly built the one tonestack I knew how to build.

I appreciate all the help.

[sluckey]

I would use the other half of the 12AX7 as another gain stage.

[Pochie45566]

I would use the other half of the 12AX7 as another gain stage.

Yeah, Right now that gain stage is being used fro the microphone channel which will never be touched .

ummm just checking, id to that by connecting the grids correct? something like that. because their plates and cathode resistors are already the same.

[sluckey]

I'd start with this. Should get a lot more gain. Maybe after this is working, fine tune by replacing the plate resistors and cathode resistors. Maybe add a bright cap to the VOL pot.

[tubenit]

Just another option.  Not necessarily "better".  With Jensen speaker and lots of other differences, it will never sound like a Marshall, but could be a fun amp?

With respect, Tubenit

** EDIT:  Corrections made based on Reply 7 & 8

[sluckey]

Just another option.

That option only has two gain stages before the PI, just like the original circuit. Gain is gonna be low. One more issue... You must have a cap between the tone stack and the grid of that PI to prevent upsetting the bootstrap bias on the PI.

[mwelch55]

I think the schematic you posted seems to have an error.  The .01 coupling capacitor on the top half of the Phase Inverter should be connected on the tube side of the 68k resistor instead of the power supply side.

Just another option.  Not necessarily "better".  With Jensen speaker and lots of other differences, it will never sound like a Marshall, but could be a fun amp?

With respect, Tubenit

[PRR]

> we cut out the tone knob of the silver tone and used the gap made to install a full marshall 2204 tonestack.

The Silvertone lets all the lows-mids right through, only trimming the highs. (With other factors leading to a bright amp, this allows a range from bright to mellow.)

The Fender (even if it says Marshall) cuts *everything* down about 7:1, then adds-back bass and treb (often mids) to taste.

So from the start you have thrown away 7X of gain which is significant.

It is suggested you add a gain stage. This may be gain of 50, far more than you need just to make-up the added loss. Of course too-much gain is not such a problem as not-enough gain.

[Pochie45566]

So, as recommended I

Removed tone pot and cap, removed 330k mlx resistor, removed mic input from pin 7 of v1 and i connected pin 7 of v1 to the wiper of the volume pot.

extra info, This amp mustve been modified to have a single volume pot aftermarket.

right now both .01 caps are connected going into the tone stack, out of the tone stack going into the VOL pot, wiper of the vol pot has the pin 7 of v1 and connected to pin7 v2, and the last leg of the pot is grounded.

Amplifier still won't distort.

so how about adding another gain stage by connecting pin 7 of v1 to to right after that .01 cap on pin 1? then just taking the plate of that second part of the 12ax7, going through the tone stack then into the  vol pot

[Pochie45566]

So I tried that, just taking the plate off of the first part of v1 after the coupling cap and putting it into the grid of the second part(pin 7) then from that stage into the tone stack and then to the volume pot. no sound.

[sluckey]

You ain't doing something right.

[Pochie45566]

You ain't doing something right.

like in concept its correct? just a wiring issue?

[Pochie45566]

Im lost to why I'm not getting any signal. even now the power on light is just flashing once then going off. the tubes all glow, it was dead silent at first then it started just making static, old caps for the noise?

I have my two instrument inputs going to the grid pin 2, pin 1 right after the coupling cap is going into the second grid pin 7, then from the plate of pin 6 after the coupling cap I go straight into the tone stack then to the volume.

I've checked the wiring a few times all seems to be well. ideas?

[shooter]

read this;

http://www.valvewizard.co.uk/dccf.html

I like to drive a "big" TS with the DCcf and 1/2 AU7 for recovery

[sluckey]

At this point it would be helpful if you would measure voltages for C17A, B, and C, as well as voltages for all tube pins. Post the results here and we'll look for clues. My strongest suspicion is that you have made a wiring error, maybe even unknowingly.

[Pochie45566]

V1:
1 - 61
2 - -92 mv
3 - .4
4 - -340mv
5 - -340mv
6 - 40
7 - 190 mv
8 - -330mv
9 - -330mv

V2:
1 - 101
2 - 67
3 - 67
4 - -340
5 - -340mv
6 - 158
7 - 0
8 - -330mv
9 - 330mv

C17C - 213
C17B - 188
C17A -166

Didn’t measure power tubes bc they aren’t of issue here. V1 voltages

V1 seems to be of issue, and all c17’s seem to be very low

[shooter]

9 - -330mv

I'd pull the tubes, verify ya got 6.3vac at tube side of socket
turn OFF discharge
ohm the cathodes of both V1&2 to ground n post
ohm any of the pre-power-rail cap+ to ground and see where it starts, like 5K climbing to infinite

[Pochie45566]

Fixed that last issue, v2 tune socked decided to get dodgey. I got the second stage working, was way too gainy so I lowered the second plate resistor to 100k and it helped a lot but there’s a noise (see video) when at higher volumes. I suspect that’s related to having too much gain but it doesn’t sound like that, maybe try lowering plate resistor on v2?

It’s like a hissing when you play a single note