Damn near started a fire in my Hot Rod Deluxe

[xtian]

ought to be fun de-soldering all 8 points on them.

Clip the pins before desoldering. Makes it easy, with a basic soldering iron.

[Oldmactech]

Followup:

Made some progress, replaced all 3 IC’s, fired right up, both channels function, reverb back, all controls functioning. Sound is loud, maybe little funky. Extra drive button caused motor boating once then was normal? Maybe since I don’t have the footswitch?

One bit of concern-when I turn it off there was a fuzz tone like decay with hum. Typically when it goes of, just goes quiet. I’ll take some voltages later, re-inspect my IC soldering for sloppy.

Thanks to all that gave me sound advice.

[nevetslab]

This is the first report I've heard about a Hot Rod Deluxe or Deville motorboating in the More Drive mode. Lack of foot switch wouldn't be cause. I'd have to go back to read your initial post(s) to see if you still have the original Illinois Filter Capacitors in the amp. They are known to go bad and cause issues, while I've never seen one motorboat.

All of the Hot Rod series amps in our rental inventory at CenterStaging, LLC in Burbank have had the gain reduced a bit in the More Drive mode. It's a simple change. I've added 604 ohm resistors (560R or 620R also work) in series with the cathode caps C8 & C9, and changing V2 from 12AX7 to a 12AY7. Still yields plenty of additional gain in the More Drive mode, while no longer ripping your ears out.

[Oldmactech]

Thanks. The filter caps were swapped.

This thing is stiill weird and unpredictable. Yellow drive switch lights before switching out of standby (with drive switch not engaged). After playing clean for 30 seconds or so the drive switch goes off acts normal switching to drive (yellow), more drive (red.) Once the more drive caused a loud bellow (best I can describe). The yellow drive light reacts to chopstick probe so it may just be loose but wouldn’t be on with no switch would it?

Clean channel sounds lousy. Almost wondering if the speaker is blown. Highs ok, low E, A awful. Tone controls all function, don’t help much. Drive channel sounds ok.
Take it apart I guess.

[nevetslab]

Thanks. The filter caps were swapped.

This thing is stiill weird and unpredictable. Yellow drive switch lights before switching out of standby (with drive switch not engaged). After playing clean for 30 seconds or so the drive switch goes off acts normal switching to drive (yellow), more drive (red.) Once the more drive caused a loud bellow (best I can describe). The yellow drive light reacts to chopstick probe so it may just be loose but wouldn’t be on with no switch would it?

Clean channel sounds lousy. Almost wondering if the speaker is blown. Highs ok, low E, A awful. Tone controls all function, don’t help much. Drive channel sounds ok.
Take it apart I guess.

I'd be guessing you have more than one fractured solder joints on both the main PCB (which is a PITA to extract) and the Tube PCB. You'll need very bright light and magnification to see the radial fracture joints where the solder has separated from the component leads. I find the pot terminals, the input jacks, the Foot Switch Jack, the Preamp Out & Power Amp input jacks with these fractures, all the high current connections, which include the area you've already had to work on...the 5W zeners for the +/- 16V supply, those 470 ohm/5W dropping resistors, the bias pot, the filter caps associated with that +/- 16V supply, the main buss caps' connections. Fender has made variations in their PCB productions, where there's plenty of pad size for the filter caps, but the chose to only expose a tiny little circle in the middle and plate those, so very little solder pad is present to solder the cap leads. I've had to unsolder those cap leads, then scrape away teh solder mask and re-tin the pads, then fold the cap leads back down and solder them into place again to get proper solder joints. I spend a fair amount of time inspecting and repairing anything that looks shabby. AND, beware....the PCB quality on the Hot Rod Series is piss poor. Solder pads lift with the greatest of ease, so be patient and exacting. I've had broken traces separate from the component solder pad before on these amps, with behavior as you've described. Once all have been found, all the amps in our rental inventory behave well.

And, those hard ribbon cables that tie the main PCB to the Tube PCB are known to break all too easily.

As to your sound.....being able to patch signal directly into the Power Amp Section helps isolate where problems are occurring. I will always disconnect the speaker plug, and connect it to my Test Oscillator (which will drive speakers directly with warble-sine wave, much easier to listen to than pure sine, and often bust bad speakers, as well as speakers/baffles whose mtg hardware is totally loose and resonates like crazy. When all else is right, then I'll reconnect it to the amp, of course.

[Oldmactech]

Thanks, I don’t have a signal generator.

I did connect a known good external cabinet and it has the same distorted sound. Seems mostly the lower tones, lower open E, Open A etc. Sounds honky, dirty, fuzzy, brittle. Etc.

[Enzo]

I've added 604 ohm resistors

OK, now exactly WHY would you (or anyone else for that matter) have 604 ohm resistors in stock? I can see maybe 1760 ohm resistors or even 221.4k, but 604?

[nevetslab]

OK, now exactly WHY would you (or anyone else for that matter) have 604 ohm resistors in stock? I can see maybe 1760 ohm resistors or even 221.4k, but 604?

Prior to changing V2 to a 12AY7, when I was empirically adjusting the gain reduction on the two V2 cathode circuits, 600 ohms sounded closer than 560 ohms or 620 ohms. So, I had settled on 604 ohms. Doing that exercise with a 12AY7 in place, the difference was much less between those nearest values. butm, of course, either value will do...........it's just a guitar amp, after all.

[Enzo]

Of course I was just poking fun, but how is it you have 604 ohm resistors in stock? Is that a standard 1% value and I am just not aware?

[nevetslab]

Of course I was just poking fun, but how is it you have 604 ohm resistors in stock? Is that a standard 1% value and I am just not aware?

After I settled on that 604 ohm value, I had ordered 50 pcs during a Mouser Parts Order, so I've had them on hand ever since. I think I re-ordered as I've put the mod into all of our rental Hot Rod Series, along with those at AuntieM over in Monrovia, nearby (near Pasadena)...another major backline gear & sound system rental facility.

[Oldmactech]

Interesting-don’t think I’ll try that.

So, today I went over some solder joints on the tube daughter board and the sound quality seems to have improved a bit, no idea specifically why.

Oddly the yellow drive light still cones on and stays on but only the clean channels makes sound until 15-20 seconds into playing the yellow light goes off and now both drive and clean channels function including yellow light and red “ more drive” light.
Almost like it needs time to warm up. One of the IC’s I replaced not making correct contact?
I am not using a pedal switch but after the 15-20 second warmup there is an audible (not amplified) click from the PCB, until the initial period no click is heard.
Thanks.

[g1]

Monitor your +15V during warmup, then do same for -15V.
Let it cool between, so you have the same delay before the click.

[Oldmactech]

I’m sorry, would that be on the ICs to look for +/- 15v?

[g1]

Sure, that would be fine. The voltages should come up pretty much instantly when power is turned on.

[Oldmactech]

Went through and inspected solder on both PCB’s and some of the connections have ne a little puzzled. More than one have pads essential close enough to touch each other but with my poor eyesight, not 100% certain. I am assuming they are on the same circuit verified by shining a flashlight through the board to see the trace.

R-57 and R58 on the tube PCB did not seem to make a proper connection so I reflowed them. Previously that tube V3 wasn’t lighting, after reflow, cane right up although with a different 12ax7. Initial playback sounded better but the boss that controls the household volume denied he a long play session.

D likely replace r57/r58 if I could just pick them up in Atlanta area. No such luck.