V1 voltage at plate in JTM45s

[5F6-A]

Hello,




This is my amp
Specs:
- JTM45 ( 5F6-A ) clone amp with a couple of Plexi era twists
- Made by the same guy who builds the amps for Carl Martin
- Hand wired, all point-to-point using terminal strips a là Hiwatt
- Combination of vintage and regular Sozo and Auricaps coupling caps
- Valves; 2 x KT66 GEC, 2 x Mullard ECC83, 1 Philips ECC83 with matched triodes for the PI, 1 x Philips GZ34.
- Parallel FX loop with mixing pot and gain reduction switch
- Cathode bias operation switch
- Master volume pot
- Obsolete Electronics JTM45 repro output transformer wired for 16 ohms.
- Black Tolex covered
- 2 x 12” semi-closed cabinet, same tolex as head with two handles a là vintage VOX and BluesBreaker grille cloth.
- Weber Blue Dog and Silver Bell alnico speakers. 12”.

my JTM45 clone originally read 170 VDC, I gad it modded to 200 VDC on the plate at V1 but I find it a bit hard to my ears.
 I've read that 150-170 VDC would give me a softer sound. I find the actual sound @ 200 a bit dry for soloing....

To make matters worse another builder I've talked to reckons that 200 VDC is still low sugesting a higher figure from 225vdc to 250vdc.

What do you think??

[hamfist]

I don't know what the recognised "wisdom" on this matter is, but I've played around with my pre-amp plate voltages, and I don't really hear that much difference tonally. Lower voltages seem to give a bit more gain though.

[horsehead]

I still say that that is one of the single most beautifulk amps I've ever seen

[5F6-A]

I still say that that is one of the single most beautifulk amps I've ever seen

cheers... it's a great amp. Sounds great... I just fell it could be fine tuned a bit... yes, the almost never ending tone quest  :D

[gwEm]

i think plate voltage affects the tone quite alot - i experimented with it on my 2204. higher gives greater tightness in the low end, and more headroom. you get more saturation with a lower plate voltage, but the extra softness can turn to fuzziness. i personally prefer higher plate voltage.

i seem to recall twinfan's laney has an ultra high plate voltage.

[hamfist]

i seem to recall twinfan's laney has an ultra high plate voltage.

I suspect that is probably the B+ for the power valves. Pre-amp plate voltage is not something I see discussed a lot (and I do hang out in some fairly geeky forums !).

[gwEm]

i seem to recall twinfan's laney has an ultra high plate voltage.

I suspect that is probably the B+ for the power valves. Pre-amp plate voltage is not something I see discussed a lot (and I do hang out in some fairly geeky forums !).

a very good point - and you may be right, although obviously the two are related. i haven't tried adjusting the two independently.

[martinw]

Higher preamp anode voltages give more clean headroom (all else remaining equal) and vice versa.
It's not particularly sensitive in my experience, and it's down to taste, there is no right and wrong.
150-170 is a bit low for may taste, and IIRC, mine are in the 220V region. I prefer the "sparkle" that you get.

[Twinfan]

Just to confirm, my Klipp has crazy high voltages on the EL34 power valves.  550v I think?

[martinw]

It's 600V!  :o

[Twinfan]

:o

[hamfist]

It's 600V!  :o

 :euuuh:   Blimey !!

[5F6-A]

I'm measuring voltage at the Plate (pin 1 or 6) on the pre amp tube,
so a voltage of 150 - 160V is not that unusual and indeed the higher the voltage generally the more headroom, treble, and stiffness to the sound.

[hamfist]

I'm measuring voltage at the Plate (pin 1 or 6) on the pre amp tube,
so a voltage of 150 - 160V is not that unusual and indeed the higher the voltage generally the more headroom, treble, and stiffness to the sound.

Correct.