Ok here's a :da question...
anyone recognise this mod - it's what's on the front end of a JTM45 clone...
http://images.lilypix.com/albums/use...ormal_both.jpg
:D
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Ok here's a :da question...
anyone recognise this mod - it's what's on the front end of a JTM45 clone...
http://images.lilypix.com/albums/use...ormal_both.jpg
:D
I don't recognize it, but I think I know what it is doing.
In the original schematic, one side of V1 amplifies the two normal inputs, the other side amplifies the two tremolo inputs. They share a cathode resistor so are configured to have the identical gain and low end frequency response.
In the mod you depict, the cathodes are split up and have separate bias and bypass capacitors. So one channel now has a 1K5 bias resistor with 50uF bypass cap which is pretty much full low-end band width (rolloff is a 2 Hz) with less "stiffness" from the original design and about the same gain.
The other channel has lower gain controlled by the 820 ohm resistor until above 285 Hz where the capacitor bypasses the cathode resistor.
I can't tell from your diagram which channel is affected, but the affected channel would have reduced bass response.
If you are interested I could model this in a circuit simulation to estimate how the gain is changed.
This does away with the Tweed-style channel interaction, if I'm reading this right.
As far as recognizing it, it looks like your handy work, Rob. I'd recognize that layout style anywhere...on TFF. :D
Thanks for the shout on a simulation - 'cause then at least we'd all know why... the reason I asked is that we have a weird thing going on with this amp - and the buck stopped here compared to other designs - and on the scope - we get a stable waveform out of the backend until we get to just over halfway... when we look at the screens on the first tube we find that the signal is clipping way earlier than that - the only place this amp deviates from the 5F6A-JTM45 apart from the classic places is at this point - and some sort of 'gain enhancement' is usually the culprit where such deviations are made - as far as I've ever found anyway - being a pup at this game - but yer Teej - it was quicker to take a snap of a modded .dwg than otherwise - thanks for noticin'... :D
We'd sure like to see the back end of it - it's been here for months - we've replaced a pair of RCA EL34's that were red-plating, the original (fried) choke with a MM, a curious F&T AZ series that appeared to be repaired then installed - and have an amp that's still not right - chock full of carbon comps - etc... etc... they should have a smilie that's holding a gun to his head :D :D
This is what does that on a 5e3:Quote:
Originally Posted by NTBluesGuitar
http://www.lilypix.com/photos/data/7...344_p41979.jpg
Man, why would you want to do that to a 5E3?!
Ah! I see now.Quote:
Originally Posted by CJ Neel
I figured either you didn't know or you were gonna let me hang to dry for a while... and I didn't for a minute think you didn't know :D :D
I suppose I was more wonderin' whether this was a problematic hack that someone else had seen somewhere... I 'd not seen it done this way anywhere else... I'm not convinced that it works either... really appreciate the shout! ... :D