Hot Rod Deluxe low power amp output

[52 Bill]

With the 4 mV signal applied to the input and all controls but reverb at 50%, the amplitude on the power tube plates (pin 3) is 14.0 VAC (V4) and 14.2 VAC (V5). If I increase the MASTER to max then V4 increases to 74 VAC and V5 increases to 79 VAC.

When you increase the master to max and get about 750mV of signal at the input of the power amp, you get 75 vac at the power tube plates, which is more than the listed 66 vac.

Have you checked the speaker and wiring, specifically the jacks?

Again all of the dc power supply voltages are low. Can you see any reason that they fluctuate?

[Tone Meister]

Bill, I've done all my testing with a known good speaker and speaker cable.

Using the preamp out of a second amp into the HRD power amp in produces what feels like full power through the exact same speaker. But using the preamp out of the HRD into the second amp produces the same anemic output through the power amp of the second amp.

When I performed the OT test, I took the opportunity to thoroughly clean and meter-test both the main speaker and extension speaker jacks

[52 Bill]

So we're back to the preamp.

Yes, the NC closed contact (R18 to R28) has continuity

What about the NO contacts (R18 to R20 and R45 to R28)? This can be tested with the amp in standby.

[Tone Meister]

So we're back to the preamp.

What about the NO contacts (R18 to R20 and R45 to R28)? This can be tested with the amp in standby.

With amp in standby
R18 to R20 = 0.3 ohms
R45 to R28 = 27 ohms

Swapped out the (good?) phase inverter tube and voltage increased substantially at the power tube plates (from ~14V to ~48V) with the same setting on the master volume. Incrementally swapped out the remaining preamp tubes, but V3 was the only one that produced an amplitude difference at the power tubes. I think the power amp is healthy now.

[52 Bill]

With amp in standby
R18 to R20 = 0.3 ohms
R45 to R28 = 27 ohms

Try monitoring the R45 to R28 contact while turning on and off the drive mode. See if the resistance lowers or goes higher as you exercise the contacts.

For grins, read the resistance from R28 to R40. Meter test diodes CR1 and CR2.

[Tone Meister]

Try monitoring the R45 to R28 contact while turning on and off the drive mode. See if the resistance lowers or goes higher as you exercise the contacts.

For grins, read the resistance from R28 to R40. Meter test diodes CR1 and CR2.

With amp off
CR1 and CR2 pass the diode test
R28 to R40 = 0.6 ohms

With amp in standby
R45 to R28 contact measures 27 ohms in Yellow mode. No change in resistance when switching to Red More Drive mode. Resistance increases to 59 ohms when Normal channel is selected

[52 Bill]

With amp in standby
CR1 and CR2 pass the diode test

R45 to R28 contact measures 0.03 ohms in Yellow mode. No change in resistance when switching to Red More Drive mode. Resistance increases to 104 ohms when Normal channel is selected

R28 to R40 = ?

So the earlier 27 ohm reading was wrong?

The R28 to R40 is the resistance of the power amp in jack switch. The amp does not need to be turned on for that reading.

[The Dude]

With amp in standby
CR1 and CR2 pass the diode test......

You shouldn't use the diode test with power applied (if I'm correctly understanding what you did).

[Tone Meister]

You shouldn't use the diode test with power applied (if I'm correctly understanding what you did).

Naw, I tested the diodes before powering up. Should have clarified that.

Bill, I measured the opposite side of R45 that last time, producing a different reading. It's still 27 ohms and increases to 59 ohms when the NORMAL channel is selected. NO change when switching from yellow to red modes. R28 to R40 = 0.6 ohms

Fellas, I'm tired and not thinking clearly. Been a long week and I have 5 shows between now and Monday. Gonna ding around with this in the morning before I have to leave. Power amp is doing its thing.

[Tone Meister]

OK, after doing some critical listening this morning - amp loaded with 8-ohm dummy load, PREAMP OUT to a second amplifier - I'm starting to suspect a problem in the tone stack. The PREAMP OUT to second amp scenario produces the same weak output as the HRD. Plugging directly into the second amp produces a much fuller sound.

The amp was modded previously as evidenced by orange drop capacitors at C5 and C6 and a silver mica at C7. The bass and midrange controls seem to affect overall amplitude very little. Also, the tone stack is set up like a Twin Reverb in that when all the controls are fully CCW there is no sound.

Looks like I need to peel back the main PCB and check for gremlins. This amp has seen extensive work previously and it's fair to say that not all of it was implemented by a professional.

[Tone Meister]

It'll have to wait until Monday. You reckon it'll keep till Monday?

[ElectricBlue]

I'm new, but I've read a lot on this board.
Here's a side note: The effort here is beyond commendable.

Ok, Same problem - Same product. Just a note, this thread is amazing, and electrically deep. I followed it well, but somewhere in the back and forth - I'm missing is a solution. Did they solve the problem? Again, the back and forth was more than educational. It reminded me of an old tech lesson I learned about poorly designed products. ** So I'm looking for an answer / solution. I have the same problem. But I'm leaning toward the main caps, because I think I unintentionally blew them doing something else. When I tap on the main cap, it's microphonic, but I'm getting correct voltage (I think). But I'm not confident in the product - anymore. If replacing the main cap doesn't do it - I'm done. I will move on to another product line. I'm a musician, I wouldn't take this product on stage at anywhere. It looks nice, works well (when it's working). I need reliability. I'm not a electrician. I haven't done every that has been posted. If I had - with no positive results, time to move on.

So that's my question, kinda backwards. What was the solution? Or did they move-on to something else.

FYI: In my area, they pricing at 75-90/per hour with 3-6 week turnaround, plus parts. Time for a new product, at those prices. One tech person looked at me like, do you really want to do this. Get it.

I hope someone replies. I know I new, but won't waste too much time kicking a dead product.

[nickb]

I'm new, but I've read a lot on this board.
Here's a side note: The effort here is beyond commendable.

Ok, Same problem - Same product. Just a note, this thread is amazing, and electrically deep. I followed it well, but somewhere in the back and forth - I'm missing is a solution. Did they solve the problem? Again, the back and forth was more than educational. It reminded me of an old tech lesson I learned about poorly designed products. ** So I'm looking for an answer / solution. I have the same problem. But I'm leaning toward the main caps, because I think I unintentionally blew them doing something else. When I tap on the main cap, it's microphonic, but I'm getting correct voltage (I think). But I'm not confident in the product - anymore. If replacing the main cap doesn't do it - I'm done. I will move on to another product line. I'm a musician, I wouldn't take this product on stage at anywhere. It looks nice, works well (when it's working). I need reliability. I'm not a electrician. I haven't done every that has been posted. If I had - with no positive results, time to move on.

So that's my question, kinda backwards. What was the solution? Or did they move-on to something else.

FYI: In my area, they pricing at 75-90/per hour with 3-6 week turnaround, plus parts. Time for a new product, at those prices. One tech person looked at me like, do you really want to do this. Get it.

I hope someone replies. I know I new, but won't waste too much time kicking a dead product.

Welcome to the place.

It's really easier to start a new thread, especially as I don't think this is (quite) dead yet. Your issue may superficially seem the same but the cause could be quite different. Are you saying one of the main big electrolytics is microphonic? If so, then replace it.

[52 Bill]

Welcome to the place.

It's really easier to start a new thread, especially as I don't think this is (quite) dead yet. Your issue may superficially seem the same but the cause could be quite different. Are you saying on of the main big electrolytics is microphonic? If so, then replace it.

Agree, please start a new thread for your amp, because it will probably be something entirely different to fix it.

I understand your concerns about having an amp that is reliable, but there are thousands of these amps out there being toured on a regular basis. If they were as bad as you seem to think, then nobody would trust using them and Fender would stop making them. Your amp has a problem. Once you fix it, it will work just fine.

[Justin Thomas]

Agree with Bill & Nick - start a new thread. Also, will ask: what's the definition of "my area?" Kinda sounds like MY area, too. I get at least some of my business because I don't have a 6-week turnaround.

Putting your location in helps, because you might live right next door to someone here...

Justin