jtm 45 build issues

[Oregonblues]

Im trying to finish up a jtm style build built off the tube depot and ceritone jtm45s, currently I get sound from the amp but super super low volume even when fully cranked on all knobs and fully cranked it is pretty distorted , the tone stack dosent do much but does alter the tone somewhat

current voltage readings are pretty close to the schematic, any help or things to look for would be great,

1st 12ax7

Pin 1: 211v

Pin 3: 1.75v

Pin 6: 209v

Pin8: 1.75v

2nd 12ax7

Pin1: 185v

Pin3: 1.07v

Pin6: 318v

Pin8: 187v

Phase inverter 12ax7

Pin 1: 243v

Pin3: 43v

Pin6: 230v

Pin8: 43v

1st el34

Pin 3: 421v

Pin4: 422v

Pin 6: -41v

2nd el34

Pin3: 421v

Pin4: 423v

Pin6: -41v

Gz34
Pin 2: 424v
Pin 8: 424v

[ViperDoc]

Check all solder joints.
Make sure you have a clear and clean preamp ground connection.
What are your power tubes biased at (cathode current) and what type of tubes are you running? EL34? KT66?

EDIT: I see you said EL34. What is your grid voltage on pin 5 of the El34? Are you using pin 6 to run your grid stoppers to pin 5 (grid pin)? Pin 6 is an NC connection on EL34 tubes.

[xtian]

Do you have a signal generator? Scope?

[Reeltarded]

Moderate all controls to half leave volumes at 0. With insulated tool start at the PI input and tap signal path backwards toward inputs. Strong tick?

Weak similar tick in lots of places: bad preamp grounding
Strong tick then very much weaker toward inputs the problem is between the test points
Strong tick all the way to the channel coupler/plate junctions look at input and volume control grounds.

[bepone]

Im trying to finish up a jtm style build built off the tube depot and ceritone jtm45s, currently I get sound from the amp but super super low volume even when fully cranked on all knobs and fully cranked it is pretty distorted , the tone stack dosent do much but does alter the tone somewhat

you have probably misswired, A1-Ub+-A2 wires

[LOUDthud]

I suspect miss wired input or speaker jacks.

Ohm checks with power OFF.
Plug a cable into one of the speaker jacks. Ohm across the free end of the cable. You should see a very low reading close to zero.

Plug a cable into one of the input jacks. Measure Ohms across the free end of the cable. You should see something like 1 MegOhm or 128K Ohm.

Ohm from the tip of the free end of the cable to pin 2 or pin 7 or the first 12AX7. You should measure 68K or 34K to one tube pin and a high resistance to the other pin.

[Oregonblues]

thanks for the suggestions so far, I checked the input jacks and speaker jacks , wired correctly and ohm out proper values aswell, decided to rebuild using only the tube depot jtm45 layout except I left out the NFB mods and the solid state rectifier, with the new layout the voltages are still within tolerance and I reflowed the joints on everything so far, I do get louder volume/noise from the guitar but the second its above a whisper it starts to oscillate/motorboat type of sound,pulling the second 12ax7 kills the noise but I swapped with a known good replacement and still no luck, parts test out fine but might try swapping the caps on those and rechecking the resistors in the morning,my grounds all also all read out continuity but im going to try to reflow them again just in case, my scope is unfortunately down at the moment

[dorrisant]

I may be wrong, but have you tried to reverse the OT primary plate leads. I don't know if you have NFB connected. If you do not have it connected then disregard.

[Oregonblues]

I may be wrong, but have you tried to reverse the OT primary plate leads. I don't know if you have NFB connected. If you do not have it connected then disregard.

ah yes I forgot to mention I have tried that with no change, I got slightly better results now after swapping the mica cap that bridges the phase inverter plates but still oscillating

edit: it does vary some with the volume and tone controls but doesn't really get louder with the volume, the bass really changes the tone and if the oscillation is going on and I touch either of the grid pins on the phase inverter with my DMM the oscillation either goes away if it was happening or it starts it, the amp is silent with no signal going through it with volumes on 0 and only some high end hiss when the volumes are cranked,
bias set right at 34mA on the el34's I forgot to mention as well

[LOUDthud]

All the Voltages in post 1 look good.

With all pots set to 5, touching a DVM probe (other probe grounded) to the Grids (pins 2 or 7) of the 12AX7s should produce a clicking or hum through the speaker. Touching 2 and 7 of the PI should produce loud clicks.

I can't help but think you may have a short at the speaker jacks. Do you have an impedance selector ? Please describe the wiring of the secondary of the output transformer. What transformer are you using ?

[dorrisant]

All the Voltages in post 1 look good.

With all pots set to 5, touching a DVM probe (other probe grounded) to the Grids (pins 2 or 7) of the 12AX7s should produce a clicking or hum through the speaker. Touching 2 and 7 of the PI should produce loud clicks.

I can't help but think you may have a short at the speaker jacks. Do you have an impedance selector ? Please describe the wiring of the secondary of the output transformer. What transformer are you using ?

Yes... like when you plug into the EXT jack instead of the MAIN jack.

[Oregonblues]

All the Voltages in post 1 look good.

With all pots set to 5, touching a DVM probe (other probe grounded) to the Grids (pins 2 or 7) of the 12AX7s should produce a clicking or hum through the speaker. Touching 2 and 7 of the PI should produce loud clicks.

I can't help but think you may have a short at the speaker jacks. Do you have an impedance selector ? Please describe the wiring of the secondary of the output transformer. What transformer are you using ?

I do get loud clicks as well as the oscillation, speaker jacks read .5-.6 ohms, The output transformer is 1750Q Hammond, wired with the orange common wire from the secondary to the sleeve of the speaker jacks, yellow to the 4ohm out labeled terminal 1 on the impedance switch, green to the 8ohm 2nd terminal and grey to the 16ohm 3rd terminal, and the impedance switch com terminal to the tip

[LOUDthud]

I do get loud clicks as well as the oscillation, speaker jacks read .5-.6 ohms, The output transformer is 1750Q Hammond, wired with the orange common wire from the secondary to the sleeve of the speaker jacks, yellow to the 4ohm out labeled terminal 1 on the impedance switch, green to the 8ohm 2nd terminal and grey to the 16ohm 3rd terminal, and the impedance switch com terminal to the tip

That certainly seems to be correct as long as there is a ground for the sleeve connection. Feedback might react strangely depending on how the transformer is interleaved if there is no ground on the Orange wire.

When you say JTM 45, it makes me think of the original circuit with no Effects Loop or any other modern nonsense. Check for resistance to ground around the pots. Should be a ground on each Volume, one on the Mid pot and one of the Presence. One end of the Treble pot might be close to ground if the Mid and Bass pots are set to minimum. Check resistance from the "mix" resistors to pin 2 of the second 12AX7.

[Oregonblues]

checked the mix resistors on pin 2 of the second 12ax7 they are in spec, I added a 100pf cap across the NFB 27k resistor with no real notable change, then I switched it for a 66k resistor and it helped some but still has oscillation, I also re flowed a few joints that I thought might be suspect, its not running away oscillation anymore but it does oscillate/nasty sounding distortion when playing through it

[Reeltarded]

1750q..

JTM 45 OT has 9k ot... 1k7.5 is for a 100.

Ok I see what you are doing. Mismatch speakers.

Sheilded wire for inputs? grid stoppers every gain stage (a and b and V2)