Dead Normal Channel - No Sound at All.

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Fender '65 Twin Reverb

The 1992 Reissue of the original '65 Twin Reverb. Different from the older model, the reissue is built with a printed circuit board and 1/4 inch footswitch phone jacks. This model features blackface cosmetics and 12'' Jensen speakers.

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Rhea deLascy-Wells @rheadelwell

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发帖于: 2024年1月21日

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Dead Normal Channel - No Sound at All.

Hi - yes its the same amp which had the transformer issue. This time, in spite of the new transformer, the normal channel is silent. No sound when I plug guitar in. Here is what I have done so far. Aside from the transformer, I have also replaced, the filter caps, all tubes, retensioned the tube seats, cleaned seats, pots and jacks. The only sound I will get is when I run the guitar lead across my hand. Note, the guitar and lead works perfectly on the vibrato/reverb channel. What have I missed?

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@rheadelwell Can you upload sone pictures of the circuit board(s) inside? 在已经存在的问题里加入图片

由 Andrew S 完成的 2024年1月24日

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jayeff @jayeff

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Hi @rheadelwell

Is the V1A valve glowing or warm indicating that the valve has power at least to the valve heater?

Have you checked the V1A anode voltage is OK? It should be the same value as the V2A anode voltage

Does operating and releasing the Bright switch affect the audio when in Vibrato/Reverb mode and also Normal mode?

If operated it will turn Vibrato/Reverb off but not Normal

Check capacitor C18 is OK as well and not open circuit.

Everything after C18 is common to both the vibrato and normal inputs.

Here's the schematic that may help.

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Hi @jayeff so I have waltzed around the circuitry of V1 with a multimeter. All components measured correctly except for R4 which is on pin 1 of V1. R4 is supposed to be 100K however reads OC. This is on one of the anodes, so I would say that no voltage is reaching that this causing only half the tube to show voltage. Therefore the voltage is incorrect. Comparing to V2 where all measurements are correct. I did check C18 which was ok. So I'd say I have found the problem, or should I check anything else. Thank you for all your help to date.

由 Rhea deLascy-Wells 完成的 2024年1月23日

@rheadelwell

I'd say that you've found the problem, if it is the only one. You'll find out when you fix this one and then test if it works

No voltage on the anode of a valve means that there's no current flowing from the -ve cathode to the +ve anode of the valve, so no output from the valve

The input signal is on the grid of the valve and this directly affects the signal current leaving the valve i.e. output signal is an amplified version of the input signal.

Just curious as to why you unaccepted my answer though. was it not helpful at least to warrant an upvote score?

由 jayeff 完成的 2024年1月23日

@jayeff, sorry that was entirely unintentional. I'll rectify that as the answer did help.

由 Rhea deLascy-Wells 完成的 2024年1月25日

@rheadelwell

Thanks.

Cheers

由 jayeff 完成的 2024年1月25日

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@rheadelwell Can you upload sone pictures of the circuit board(s) inside? 在已经存在的问题里加入图片 — Andrew S
Hi @jayeff so I have waltzed around the circuitry of V1 with a multimeter. All components measured correctly except for R4 which is on pin 1 of V1. R4 is supposed to be 100K however reads OC. This is on one of the anodes, so I would say that no voltage is reaching that this causing only half the tube to show voltage. Therefore the voltage is incorrect. Comparing to V2 where all measurements are correct. I did check C18 which was ok. So I'd say I have found the problem, or should I check anything else. Thank you for all your help to date. — Rhea deLascy-Wells
@rheadelwell

I'd say that you've found the problem, if it is the only one. You'll find out when you fix this one and then test if it works

No voltage on the anode of a valve means that there's no current flowing from the -ve cathode to the +ve anode of the valve, so no output from the valve

The input signal is on the grid of the valve and this directly affects the signal current leaving the valve i.e. output signal is an amplified version of the input signal.

Just curious as to why you unaccepted my answer though. was it not helpful at least to warrant an upvote score? — jayeff
@jayeff, sorry that was entirely unintentional. I'll rectify that as the answer did help. — Rhea deLascy-Wells

Fender '65 Twin Reverb

Dead Normal Channel - No Sound at All.

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