vintageHIWATTconvention.com

2500 for a 1971 DR103 head and cab is a great deal if it's original

@shakti emailed ya!

I have mine wired per stock: No switch inserted or inserted with contacts connected: quiet mode Switch inserted and engaged/contacts broken: loud mode I considered reversing it so the default state of the amp is cascaded but I think I'll leave well enough alone, source some nice coax and see if I ca...

@shakti - great timing actually and funny story! The oscillation came back which was baffling. How could it be gone and then come back when the amp hasn't moved or changed? It struck me that the issue could be with the SWITCH and its cabling since it was long and coiled up and if the cable was crumm...

How do you know if you need a bias doubler?

Very happy to report that everything is fixed. It actually had NOTHING to do with the preamp. After extensive chopsticking the presence wire from the power supply board to the OT selector was a clear problem. That "Led" me to a full audit of the power section and when I installed an adjust...

excellent! ;) How damaging is PO to tubes - aka should I put some beaters in while troubleshooting layout? Or is it just an unpleasant listening experience during? I doubt layout is the issue given it's Hiwatt spec but I'll chopstick some of the wires around. Grounding I think is legit but I'll doub...

mhuss wrote: ↑Tue Apr 21, 2020 7:01 pm If we wait long enough, you'll fix everything yourself.

Motorboating is almost always bad filter caps.

Motorboating issue went away when I realized I had mis-wired something in the midst of trial & error troubleshooting. Whoops + red herring

I hoped you were right but back to where I began :) The circuit is wired up like Shakti's so basically has v3 and v4 connected like sn 894 but the v1 and v2 are JP spec. Sounds great and everything works perfectly when the boost is disengaged. When the boost is engaged I get PO squeal when input vol...

Welp, dumb mistake the 1n cap on the presence pot was hooked to the wrong side of the .047 i'm shocked it worked well for so long. The increased gain must have just brought it to light. More work to do stay tuned but that seems to have killed the squeal. Now I get a motorboat but only at FULL vol, b...

Potentially one more clue - the gain is definitely high when the switch is engaged. When it's off (single triode mode) no issues and the amp seems not loud enough for a 100w and with the switch engaged there's a very loud hiss and it's definitely full power (plus gives the PO).

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Did a clone of a JP amp a long ways back and just put an NOS RFT in v1 to get a bit more gain from it as I've found those to be pretty hot tubes. With the boost switch engaged i'm now getting parasitic oscillation at the top (3pm-5pm) of the input vol range or if the presence is up. It's not lead dr...

The earliest Hiwatts have 470k resistors on the inputs rather than 1M which obviously impacts the input impedance.

Is it better to replace the 470k's with a 1M for playability/sound (keeping the 470k's for originality)?

Thanks Mark - I'd hate to ruin the amber tophat indicator so I'll probably leave it dim. I've got a spare NOS Radiospares red one but I've never seen another amber!