help with new jtm45 build please, no sound from input #1

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jmann
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help with new jtm45 build please, no sound from input #1

Post by jmann » Wed Jan 27, 2016 12:59 pm

Hi all, Im having problems with this build and not sure whats going on. Im a few hours away from a large hammer and calling it good!
Anyway, I have built 6 amps not including this one. Not experienced by any means, but never a problem with any of the other builds ranging from a 18watt marshall to tweed deluxes and bassmans.
Problem is, Im not getting any sound from the #1 set of inputs on the amp. The volume #1 pot would produce a large thump through the speaker when turning it as it passed about the 3 position. I thought mabye I overheated a pot when soldering the buss bar so I replaced the pot and it behaves the exact same. I have retraced everything and am at a loss. I have attached voltage charts of readings of my amp with both the kt66's out and in the amp. Please let me know if I can provide any other pics and thanks in advance for looking.

Image

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danman
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Re: help with new jtm45 build please, no sound from input #1

Post by danman » Thu Jan 28, 2016 4:03 pm

I would look at the wiring on the input jack for the problem. Is it both hi and lo jacks on channel one that do not work? Have you tried a new tube in V1? Do you have continuity through the circuit from the tip of the jack to the grid of the v1 socket? After the volume pot the signal mixes with channel 2 at the 270k mix resistor junction so I would really check everything before the volume pot. Also check the ground from the volume pot.

jmann
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Re: help with new jtm45 build please, no sound from input #1

Post by jmann » Thu Jan 28, 2016 8:01 pm

Thanks danman. I'm guessing your responding to my same question on tdpri. I'll just default to that thread since there seem to be a lot more help over there and will update on that board. Many thanks for your suggestions.

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neikeel
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Re: help with new jtm45 build please, no sound from input #1

Post by neikeel » Fri Jan 29, 2016 12:26 pm

jmann wrote:Thanks danman. I'm guessing your responding to my same question on tdpri. I'll just default to that thread since there seem to be a lot more help over there and will update on that board. Many thanks for your suggestions.
Sorry, not glued to the computer, you posted on Wednesday evening :wink:

If channel 2 works you know the cathode cap/resistor is ok, and you have plate voltage on both triodes so it has to be either the grids (68k resistors and the grid wire from their apex - check it has not fallen out under the board - hopefully you looped the wires up through a perforated board and wrapped the wire around the terminal turret?)

The next thing is to check you have not reversed the wires from the pot between the coupling cap and the mixer resistor. Even if the mixer bypass cap is duff you should still get some sound.

As ever with this sort of thing a couple of really clear photographs helps us hugely, as does the voltage chart that you already posted.
Neil

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