trinityamps.com

It looks different than the standard LTP you see in Marshalls ect. Anyone care to discuss this?
Stew

The sIII or Marshall style is the more typical AC coupled long tailed pair type PI.

The Triwatt is what Hiwatt used, the DC coupled long tail pair.

They are discussed on Merlin's Valvewizard site to get into the details but it seems the main difference is that the tube in the AC coupled version is cathode biased.

If you look carefully at Hiwatt schematics from the '60s and early 70s (as well as the Triwatt's) you will see that there is in fact a DC-coupled path between the preamp stage after the MV, to the cathode follower, and then to the PI. From the late '70s on, the cathode follower was removed from the path and that triode was instead used purely as a voltage regulator to bias the PI, which made it a fixed-biased PI. Dave Reeves' didn't seem to be interested in following other peoples' guitar amp designs, so his own designs are quite unique in a number of ways.

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Great tones come in small glass jars!

So ..is the fact that the PI is direct coupled to that catode follower the reason why there is only 1, 1meg resistor in the pi circuit instead of one on each grid?
Another question about LTPs in general...Is the NFB (on marshall style )coupled to the second grid AND the common cathodes as well? ..that's the way it looks.
Stew

It's actually because the PI is DC-coupled directly to the stage in front - it doesn't have to be a cathode follower. Take a look at Merlin's example at the bottom of the page on www.freewebs.com/valvewizard/dcltp.html


Yes, that's right. Most Marshall style amps and a few F*nders inject NFB into the PI at two points. The main NFB is provided by sending the fed-back output signal into the second or 'B' input of the PI. As an option, you can also make the PI appear to be better balanced by injecting some feedback into the PI tail. This was yet another misguided attempt by Leo Fender to make guitar amps sound cleaner.

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Great tones come in small glass jars!

Great~
Thanks alll!
Stew

hey your pretty smart
Don't knock me ; I'm in mood swingds thanks the the experiments;
Oh well
It was still funny!
LJ