Josh's 18W Tremolo TMB Builds

[TriodeLuvr]

Btw, I found out that putting a 12at7 in the PI the volume is substantially less compared to a 12ax7.

That surprises me. According to the math (simulator), the difference in this application is only about 2.5 dB. Are you using the "standard" Marshall PI circuit?

Jack

[Bieworm]

Btw, I found out that putting a 12at7 in the PI the volume is substantially less compared to a 12ax7.

That surprises me. According to the math (simulator), the difference in this application is only about 2.5 dB. Are you using the "standard" Marshall PI circuit?

Jack

Yes standard PI.. but only playing on lowish volume it's pretty noticable.

[crgfrench]

The gain of a LTP is equal to the gain of a single gain stage for a given tube. The mu of a 12AX7 is 100 and the mu of a 12AT7 is 60. So that's why the 12AT7 LTP is lower volume.

[Bieworm]

Here is a soundclip of my tremolo TMB reverb on full blast. Volume and gain on 10. Incredible how it cleans up on the guitar volume pot!!!

https://www.dropbox.com/s/23h9ol4lwyy9r ... t.m4a?dl=0


And here is my rockin'bird .. same deal, but creamier.. the tremolo TMB is nastier and superior to my taste.

https://www.dropbox.com/s/4ztce46vyo1e8 ... t.m4a?dl=0

20210220_142030.jpg

[JMPGuitars]

After highlighter testing, I tested the voltages, and everything looks great, except my B+ is slightly low because I used a 3.3K instead of a 2.2K. I'll swap that out when I get some more 2.2Ks in stock (or find the ones I swear I ordered ). I also need to up the wattage on the cathode bias resistor, that thing is fairly hot. After I do that, I'll do some more testing, and then add the FX loop.

BTW- I'm slightly surprised nobody noticed that I didn't solder the ground wire on the intensity pot. Good thing I check connections during highlighter testing.

[Bieworm]

What wattage did you use on that resistor?
I have got 5W in my tremolo TMB 's...
Or does it have anything to do with the 36W power compared to 18W?

[JMPGuitars]

That resistor is about 8W. But yes, it's because of the 36W amp. Normally I use a 20W resistor there on 36W amps, but 20W is overkill, so I wanted to see how hot a lower wattage resistor would get.

[Bieworm]

That resistor is about 8W. But yes, it's because of the 36W amp. Normally I use a 20W resistor there on 36W amps, but 20W is overkill, so I wanted to see how hot a lower wattage resistor would get.

Good!!! I was starting to get worried

[JMPGuitars]

I got my double switch PCBs in:

grounding double switch.jpg

[TriodeLuvr]

The gain of a LTP is equal to the gain of a single gain stage for a given tube. The mu of a 12AX7 is 100 and the mu of a 12AT7 is 60. So that's why the 12AT7 LTP is lower volume.

The gain of a LTP is typically less than half the gain of the tube in grounded cathode (bypassed) mode. With the Presence control at minimum resistance and no NFB, the Marshall 12AX7 LTP exhibits a voltage gain of approximately 22. Substituting a 12AT7 with no other changes, gain falls to about 16.5. That's a difference of 2.5 dB. I would have thought you'd need to pay close attention to hear that.

Jack

[TriodeLuvr]

That resistor is about 8W. But yes, it's because of the 36W amp. Normally I use a 20W resistor there on 36W amps, but 20W is overkill, so I wanted to see how hot a lower wattage resistor would get.

Is that a cathode bias resistor you're discussing?

Jack

[Bieworm]

That resistor is about 8W. But yes, it's because of the 36W amp. Normally I use a 20W resistor there on 36W amps, but 20W is overkill, so I wanted to see how hot a lower wattage resistor would get.

Is that a cathode bias resistor you're discussing?

Jack

Yes.

[JMPGuitars]

I got the 2.2Ks in finally, and put in the 20W cathode resistor. Here's what it looks like now:

_JMP1974.jpg

[crgfrench]

I mean, even a 12W brown devil is overkill.

[crgfrench]

The gain of a LTP is typically less than half the gain of the tube in grounded cathode (bypassed) mode. With the Presence control at minimum resistance and no NFB, the Marshall 12AX7 LTP exhibits a voltage gain of approximately 22. Substituting a 12AT7 with no other changes, gain falls to about 16.5. That's a difference of 2.5 dB. I would have thought you'd need to pay close attention to hear that.

That difference gets amplified again in the output stage.