CDee
Hi guys,
We had a power surge at our church on Sunday and my amp stopped working >☹
Do you know any decent techies that can have a look at my Hot Rod Deluxe in the Vaal area. This is urgent as this amp gets used extensively.
Thanks in advance,
CDee ?
MikeM
Chat to Gearhead unless you already have..
TomCat
Silly question but have you checked the fuses.
Otherwise +1 on Mike's suggestion of contacting Gearhead.
Sean
TomCat wrote
Silly question but have you checked the fuses.
Never a silly question Tom, I've been caught out by that :-[
CDee
TomCat wrote
Silly question but have you checked the fuses.
Hi Tom,
I only know of the one fuse and I checked it, it looks fine...
Thanks
TomCat
CDee wrote
TomCat wrote
Silly question but have you checked the fuses.
Hi Tom,
I only know of the one fuse and I checked it, it looks fine...
Thanks
I just had a gander at the schematic and there is only one fuse on the mains side so it looks like something has indeed gone US in your amp.
When you switch on do the heaters of the tubes glow? If they do then something on the HT side may have gone faulty.
If nothing happens at all then it might be the power tranny.
CDee
TomCat wrote
When you switch on do the heaters of the tubes glow? If they do then something on the HT side may have gone faulty.
If nothing happens at all then it might be the power tranny.
The amp comes on and the valves glow (1 of the smaller valves glows a lot dimmer than the others) You can hear sound but it's very soft and very dirty. I've removed the attenuator but still the same problem. :'(
TomCat
CDee wrote
TomCat wrote
When you switch on do the heaters of the tubes glow? If they do then something on the HT side may have gone faulty.
If nothing happens at all then it might be the power tranny.
The amp comes on and the valves glow (1 of the smaller valves glows a lot dimmer than the others) You can hear sound but it's very soft and very dirty. I've removed the attenuator but still the same problem. :'(
Sounds like one of the pre tubes is US......I'm sure Gearhead could sort that out. BTW is the amp under guarantee?
CDee
TomCat wrote
Sounds like one of the pre tubes is US......I'm sure Gearhead could sort that out. BTW is the amp under guarantee?
I've had this amp for almost 2 years now and I bought it second hand. So no guarantee... ☹
Gearhead
Well Gearhead got not just a bit confused about this amp :-[
The main problem seems to be that the amp has lost quite a bit of volume after a brown-out at CD's church. As far as I know, brown-outs do not kill tube amps but they do fry solid state amps.
After rolling the preamp tubes, the conclusion was that none of those are bad. Then, checked the preamp through the pre-out and my power amp (same problem) and the power amp through my preamp and the power-in (same problem). Checked tube voltages, seems okay, Even checked speaker, aslo fine as expected.
Only figured out something that could be the problem when we checked out the schematic: opamp U1B is part of the signal chain whatever you do. Will now replace U1 entirely and see what happens...
Anyone any better ideas?
FenderBender
I also just took a look at the schematic. If the preamp out and power amp in jacks are unused (and all their contacts are working), then the signal does not pass through U1. It's possible that the signal is being pulled to ground near the junction (C13 and R40) that feeds the reverb cct and the power amp. Stick your scope on there and have a look.
Gearhead
Graeme Parfett wrote
If the preamp out and power amp in jacks are unused (and all their contacts are working), then the signal does not pass through U1.
Had a hard time figuring that out with the funny tipringsleeve setup :-[
So if it does not pass through U1, would it make sense to replace U2? The passives around that junction would not have a problem with the voltage dropping...
FenderBender
U2 could be your problem. If you remove C13 and R38 you will know if the reverb cct is sucking away the signal.
Gearhead
Okay, replaced both opamps with opamp sockets and new chips. Changed nothing about the problem, but did give us another shot at trying the pre-out main-in thing. Turns out we were wrong yesterday night: the preamp is not the problem, but the power stage gives a very faint sound when driven with my Triaxis. At 3 on the Triaxis out, it is clean and faint and at 9 it is overdriven and a little louder.
FenderBender
If you've got a spare 12AX7 for the power inverter and two 6L6s, pop them in and check.
The best way to faultfind is with a acope. Follow the signal from TP23 onwards through the power amp cct.
C28 could be a culprit. Use your scope to see whats happening on both sides of all coupling caps (and measure all values of resistors with your meter) in the power amp stage.
EDIT: Also check CR4 and CR5.
Gearhead
>☹ Given up. The fact that a clean outboard preamp is able to overdrive the phase splitter means either of two things to me:
- the power tubes do not draw their normal current so the preamp tubes see too much voltage (could have checke that btw :-[ )
- the phase splitter is fine but there is 'something' funny between PI and power tubes.
Other possibilities eliminated: biasing (measured 70mA across R66), snubbing cap C30 being faulty (removed), power tubes not getting enough voltage (measured 425V) and many more...
CDee
Thanks for all the effort Gearhead! It's really appreciated. ?
CDee
>☹ >☹ >☹
Let this be a lesson for every owner of a HRD. Do not play with the speaker input of the amp while playing live... Probably stuffed it up when I took out my attenuator.
Looks like there is a issue with this specific range where if you plug the internal speaker into the external speaker out, you get a dramatic loss of volume. So, don't be a dumbass like me... >☹ ☹ :'(
CDee
What I couldn't figure out is why the amp stopped working mid song...
Well, I actually found the root of the problem, my attenuator seems to die intermittently. I just added it again, played for a minute and then, nothing.
So that is why when I removed it the amp worked fine. When I added the attenuator in again that afternoon, I must have plugged the speaker into the wrong jack and that is where the fun started... >☹
Can we please add a "kick my own ass" smiley? :-[
Gearhead
No need to kick any asses. I have to admit it is really hard to repair an amp that ain't broken... :-\
