Deluxe Reverb 65 RI - Blown fuse now low output

[Skeeter_pdx]

I'm working on a Deluxe Reverb reissue for a friend who said it was blowing fuses. I got the amp back running again but the output seemed a little quiet, and the amp would break up earlier than I imagined it would. I haven't played a Deluxe but it seemed to have less output and lower headroom than my Princeton. He took the amp back but agreed the sound was off. Here's a list of the steps I've taken so far:

- Put a new fuse in, and with the amp plugged into a current limiter, I could see the rectifier tube arcing.

- Powered off the amp and took a look inside the chassis to look for any visible damage. Everything looked good but one of the filter caps (C35) appeared to be shorted--had a resistance very close to 0 when I measured with a multimeter.

- Replaced all filter caps and put in a new rectifier tube.

- Amp powered up without the current limiter illuminating or fuse blowing, but there was no bias voltage present.

- I found the fusibile resistor (R69) in the bias circuit had blown and replaced it with a 22 ohm resistor. I also replaced the bias capacitor (C36). Bias voltage was back and I set it to ~70% dissipation.

The amp was then making sound and functioning somewhat normally except the low output. I have tried new tubes in every position, tried a different speaker cabinet, cleaned and retensioned all the tube sockets, and reflowed a few solder joints. The issue occurs on both the normal and vibrato channels, so I assume the problem is either in the phase inverter or output sections. I am getting what appear to me to be good voltages on all the tube pins and power nodes, although I am happy to go back and provide specific numbers if that would be helpful.

If anybody has experienced a similar issue with a Fender Reissue and has any advice that would be much appreciated. I feel like I have exhausted my usual troubleshooting procedures. Would it be best to check component values and solder joints? Trace a signal with an oscilloscope? Try a different OT?

Here's a link to the schematic https://robrobinette.com/images/Guitar/Deluxe_Models/65_Deluxe_Reverb_RI_Manual.pdf

[BrianS]

Did you measure the output power as specified on the schematic?  It's good to have actual data to back up what you think you're hearing.  I know for a fact that that amp will indeed put out 22 watts RMS as stated on the schematic when it is fully functional.

The schematic has all the voltage numbers you need, including VAC of in the input signal at various points throughout the amp.  Did you set up your test procedure as Fender has outlined?

[Latole]

Remove all power tubes power amp ON with curent limiter .

[spunko]

I know it sounds kinds silly, but have you checked if the speaker is conected into the correct jack?

When you plug it into the extension jack, it gives low and distorted output.

[Skeeter_pdx]

Did you measure the output power as specified on the schematic?  It's good to have actual data to back up what you think you're hearing.  I know for a fact that that amp will indeed put out 22 watts RMS as stated on the schematic when it is fully functional.

The schematic has all the voltage numbers you need, including VAC of in the input signal at various points throughout the amp.  Did you set up your test procedure as Fender has outlined?

I haven't measured the output power but it is undoubtably much quieter than my Princeton. I got an old Tektronics scope for cheap and I'm not sure its working properly--was having a difficult time getting AC signals to trigger. Some of the AC test points I could measure with a multimeter and those looked good. All the DC test points were almost exactly what was listed on the schematic. I really wanted to get measurements of TPs 31 and 32 in the phase inverter, but without the scope I'm out of luck for that.

[Skeeter_pdx]

I know it sounds kinds silly, but have you checked if the speaker is conected into the correct jack?

When you plug it into the extension jack, it gives low and distorted output.

I just double checked, the internal speaker jack shorts to ground when nothing is plugged in so the extension jack doesn't even work on its own. Appreciate the suggestion though, its so easy to overlook some obvious causes for frustration

[AlNewman]

Check resistors around the power tubes, they were probably redplating.  Maybe blew a screen resistor or something.  Check and compare voltages across the entire amp.
You can measure resistance across both sides of the OT primary, and compare.

[BrianS]

Measure output power with your meter.

[stratomaster]

I just double checked, the internal speaker jack shorts to ground when nothing is plugged in so the extension jack doesn't even work on its own. Appreciate the suggestion though, its so easy to overlook some obvious causes for frustration

This is one of those cases where the resistances are low enough that you can't consider the shorting jack as actually shorting.  The jack has some very low but non-zero resistance--and this is in parallel with 8 ohms, so there is some amount of signal that makes it to the speaker when you plug just into the extension jack instead of the internal speaker jack.  But it's low and often distorted.

Glad this wasn't the issue for you, but the recommendation to check for this was not entirely divorced from your description.

[labb]

FWIW: I would take an audio probe and start injecting a signal at the PI and work my way back to the input. Find out where it is losing the signal. If you don’t have the probe see R.G. Keen’s audio probe at geoflex.com or maybe diystompbox.com. Whole lot like Hoffman’s listening amp in reverse

[bmccowan]

I like that audio probe approach and have a tip and a caution:
Tip - I downloaded a signal generating app to my iPad and send a signal to the probe through the headphone jack. Some people strum, or have their wife strum, a guitar to generate the signal, but this reminds me of one armed wall paper hanger jokes, and my wife is a pain to work with: "should you have your hand in there?" "how long do I have to do this?" etc.
Caution - this works well when there is no volume, or very little volume, getting to the speaker. But what is described here may be hard to detect by going through the circuit. Using both a listening amp and an audio input probe might help find the problem area.
BTW - I like AlNewman's suggestion of checking the resistors. Fender used a lot of downsized wattage rating resistors in those reissue amps. Also, if the power tubes did redplate, do you know that they are operating reasonably matched?

[labb]

I use a cd player to send to the probe.

[bmccowan]

I use a cd player to send to the probe.

A what? Just kidding.

[labb]

Guess I don’t have to tell that I am old school.

[tubeswell]

I'm working on a Deluxe Reverb reissue for a friend who said it was blowing fuses. I got the amp back running again but the output seemed a little quiet, and the amp would break up earlier than I imagined it would. I haven't played a Deluxe but it seemed to have less output and lower headroom than my Princeton. He took the amp back but agreed the sound was off. Here's a list of the steps I've taken so far:

- Put a new fuse in, and with the amp plugged into a current limiter, I could see the rectifier tube arcing.

- Powered off the amp and took a look inside the chassis to look for any visible damage. Everything looked good but one of the filter caps (C35) appeared to be shorted--had a resistance very close to 0 when I measured with a multimeter.

- Replaced all filter caps and put in a new rectifier tube.

- Amp powered up without the current limiter illuminating or fuse blowing, but there was no bias voltage present.

- I found the fusibile resistor (R69) in the bias circuit had blown and replaced it with a 22 ohm resistor. I also replaced the bias capacitor (C36). Bias voltage was back and I set it to ~70% dissipation.

The amp was then making sound and functioning somewhat normally except the low output. I have tried new tubes in every position, tried a different speaker cabinet, cleaned and retensioned all the tube sockets, and reflowed a few solder joints. The issue occurs on both the normal and vibrato channels, so I assume the problem is either in the phase inverter or output sections. I am getting what appear to me to be good voltages on all the tube pins and power nodes, although I am happy to go back and provide specific numbers if that would be helpful.

If anybody has experienced a similar issue with a Fender Reissue and has any advice that would be much appreciated. I feel like I have exhausted my usual troubleshooting procedures. Would it be best to check component values and solder joints? Trace a signal with an oscilloscope? Try a different OT?

Here's a link to the schematic https://robrobinette.com/images/Guitar/Deluxe_Models/65_Deluxe_Reverb_RI_Manual.pdf

Pop test the signal chain from back to front to find out which stage is letting you down, and look there for the problem (e.g., leaky coupling cap, cracked pcb trace etc).

[bmccowan]

cracked pcb trace

An ex-band mate has one of those amps. After about a year it started having problems with pcb trace cracks. The resulting sound degradation was similar to what you describe. He told me that he needed a magnifying glass to see them. He has had them repaired/jumpered but considers it a losing battle.

[mresistor]

If it were my amp and it was having trace crack problems with the pcb I wouldn't hesitate ripping that crap out and installing an old school AB763 DR eyelet board or even a Hoffman AB763 DR board.  The conversion isn't all that difficult if you think it through.