Hot Rod Deluxe - Mystery

[teleblasted]

Hello All: I'm a brand new member due to Googling my problem:

I was set up to play a gig a couple of nights ago with my band. I switched on my HRD as usual. The red light came on, then after 30 seconds I switched on from standby. No sound.

After messing with it (under pressure) onstage for a couple of minutes, I gave up and used a spare amp as it was time to get on with it. I did not start looking to see if all the valves were lit at the time. Later that night when I got it home, I checked the internal fuse was ok, and switched the amp on. All the valves lit up. All working ok!

I've had the amp for about four years, has never been messed with at all, and has probably done about 100 cycles of 2 hours. Unfortunately I had an amp stand collapse a few weeks back, and it horrifically dropped about 4 inches to the ground, and onto it's back. It did not stop then, and it has been used a number of times since with no problems. The amp (apart from the accident) is treated gently.

I've read some comments about plugging in the wrong jacks (which I don't think I did), overheating resistors etc. which seem to associated with performance problems rather than on or off. Now, it could just be me being dumb, but I don't think so. Has anyone got any ideas?

[52 Bill]

Welcome!

Your problem seems to be signal path related, as the power light didn't go off when the failure happened.

Two things to try are one, try inserting a spare guitar cord from the preamp out to the power amp in jack. If the return jack is dirty or oxidized it could cause the intermittent loss of signal.

Secondly, turn off the reverb and give the amp a good thump with your fist. If the signal cuts out when you do this, it means that there is something loose inside that may need to be replaced or re-soldered.

Hope this helps.

[pecorporation]

That's the "technical tap".

[Enzo]

Are you the original owner and you bought it new? Then it still has a year of warranty left. Take it in.

otherwise, anything we can tell you it needs is going to require soldering to the circuit boards. Are you skilled enough to do that?

[teleblasted]

Thanks to 52 Bill and Enzo: I read the one about the dirty return jack already on this forum (will give it a go), and no I'm not an electronic engineer (hence some ignorance) but I am a mechanical engineer, and if I can get my hands on the components all repair operations like disassembly and heat sunk soldering etc are no problem to me.

Bought the amp used from a music college as 'reconditioned'. Which I would expect would mean the valves had been changed. Fairly confident of this as it carries a proper tested and approved sticker, as you would expect from a responsible organisation.

I will open the amp and have a peer around for dry joints, scorching etc. (I've read stuff about valve mounting joints going dry). Ref the comment from Pecorporation, is there a simple way to ground out the voltages quickly, or a 'safe period' after which you would expect any potentials to have discharged? Or does this mean wear a ground lead as IT techs do? I'm not as incompetant as I sound; and I am a cautious professional (just in another field)!

[Enzo]

Grouond wrist straps are for static electricity around sensitive stuff. A wire grounding your body to the chassis is the last thing you want. All it would do is guarantee a completed circuit THROUGH you if another body part touches something live.

get a volt meter and check for voltage in the circuit.

Look in the rear of your machine. The tubes all hang down from their sockets, and the sockets are all on a narrow circuit board with ribbon cables up to the main board. Each tube socket shops up as a ring of pins poking through the board and then soldered to it.

Those solder connnections break. Look closely at them, especially the ones for the power tubes. Good idea to resolder those, certainly if any joints look cracked around the pin leg.


The tube heaters MUST light up for it to work, but seeing them lit tells you ONLY one thing about the amp - that the heaters are on. That does NOT tell you the tubes are functioning.

[guitician]

Remember the days when you would take your tubes to the corner drug store to put them on that "Tester" that had tubes for sale in it's cabinet base? My father used to do that....a lot...lol
Music store owners could re-introduce this don't you think? Especially with those Russian/Chinese tubes

[teleblasted]

Hi all,

I inspected all visible components and soldered connections visible by removal of the back, but did not dismantle the amp from the cabinet. All appears clean and well connected. Went round the valve mountings and resoldered them anyway.

The amp works on both channels but is very noisy. Lots or random crackles, scratches, and sounds like wind buffeting, plus a very loud pop when switching channels. All rise and fall with volume adjustment. I guess I did not notice this on first inspection as I had the amp at very low volume

Tried the preamp output to power amp input link with signal cable. No change there so presumably the dirty jack thing is not the problem.

Looks like I'll have to hand it over to a pro! Unless that all sounds familiar to someone.

Regards All

[teleblasted]

Hi again

I inspected all visible components and soldered connections visible by removal of the back, but did not dismantle the amp from the cabinet. All appears clean and well connected. Went round the valve mountings and resoldered them anyway.

The amp works on both channels but is very noisy. Lots or random crackles, scratches, and sounds like wind buffeting, plus a very loud pop when switching channels. All rise and fall with volume adjustment. I guess I did not notice this on first inspection as I had the amp at very low volume

Tried the preamp output to power amp input link with signal cable. No change there so presumably the dirty jack thing is not the problem.

Looks like I'll have to hand it over to a pro! Unless that all sounds familiar. Could this be just a valve?

Regards

[Jazz P Bass]

Fender HRD

You could try lightly tapping each preamp tube.
If you can make the crackling worse (or better) by tapping, that one may be a bad tube.

[pecorporation]

Sounds like a bad valve to me.

[teleblasted]

Hello Again.

I'm not one to give up easily. I bought a new preamp / phase inverter valve and tried it in each of the three positions sequentially. No joy.

I believe I can hear one of the power valves buzzing / singing very very quietly but acoustically. It's hard to tell exactly, or which one (or both) with the competing noise coming from the speaker. I'd need to travel to buy spares quickly, so can anyone tell me if that is normal? or if it's a sign of impending failure maybe? before I go to the trouble and expense of getting a new matched pair. Could this be the source of my channel changing pop, and assorted noises?

Regards to all.

[52 Bill]

Output tubes can become microphonic, but if the noise that you describe will lessen when you turn down the volume control, they are probably not the source of the noise.

It sounds like you may have a leaky coupling cap in one of the preamp stages.

When you inspected the tube socket pc board did you check all of the sockets for bad solder connections or just the power tubes?