THD Univalve
- Thread starter CJ
- Start date
Help Support GroupDIY Audio Forum:
How does it sound? I’ve been playing around with single ended lately. I built a 5f2 but put a larger power transformer and larger output transformer with 3k / 5k and 4/8/16 ohm output. taps to play with 6v6 up to el34 6550 etc. I love the sylvania 6v6 right now but have a excellent valvo el34 to play with. I’m not sure what I’m looking for but this THD amp looks impressive.
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It sounds fantastic! Got a hot and a clean input jack which switches in an extra gain stage like the Marshall 4 hole,
Power brake is like a master volume only better.
That second pilot lamp fluctuates with the music, like an La2a so we must investigate...
Andrew sold a million hot brakes but put the brakes on after covid whacked his bottom line and also because of the stress of running a small business.
Power brake is like a master volume only better.
That second pilot lamp fluctuates with the music, like an La2a so we must investigate...
Andrew sold a million hot brakes but put the brakes on after covid whacked his bottom line and also because of the stress of running a small business.
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rock soderstrom
Tour de France
capacitorless
Well-known member
I understand (but don't know 100%) that the Hot Plate is a post-OT load device. I had a UniValve a few lifetimes ago, but I never opened it up to see how he designed it.
I'm looking for photos and/or schematics of the HP standalone units. It looks like part of the circuit involves resistors on a heatsink. Maybe a fan. Some of the comments on the internet said it's purely resistive.
In CJ's photo above it looks like part of the implementation is a ceramic wirewound pot.
I'm building a Hall Amps VVR into a 5E3 type circuit, and that shunts B+ through a mosfet that is mounted to the chassis to use that as a heatsink (as you probably already know). The B+ control is a standard potentiometer in that circuit.
I'm looking for photos and/or schematics of the HP standalone units. It looks like part of the circuit involves resistors on a heatsink. Maybe a fan. Some of the comments on the internet said it's purely resistive.
In CJ's photo above it looks like part of the implementation is a ceramic wirewound pot.
I'm building a Hall Amps VVR into a 5E3 type circuit, and that shunts B+ through a mosfet that is mounted to the chassis to use that as a heatsink (as you probably already know). The B+ control is a standard potentiometer in that circuit.
Sorry, got the power brake and the hot plate mixed up, it is a hot plate and yes, ceramic wirewound , not too much power to kill on a SE but the kt88 is loud!
I bet the B+ is way up there we will find out,
I bet the B+ is way up there we will find out,
capacitorless
Well-known member
I had a Scholtz Power Brake way way back, and it too was resistive. In that case it was a rotary switch that maintained a constant load to the amp 
Doing a diy Weber Mass type attenuator at present. It won't handle the load that a HotPlate will, but should be good for 15-20w or so. I'm using a Radio Shack L-pad and the voice coil/magnet assembly from a speaker that developed voice coil rub. We'll see what transpires.
Anyways, THD stuff is built great and love the Twain/Banzai quotes!
I don't remember who, but someone was supposedly putting something like "This Amp was built using 100% Alimony" on their boards.
Edit: @CJ after further thinking, I seem to recall the 2nd lamp was part of the power soak/hot plate circuit.
Doing a diy Weber Mass type attenuator at present. It won't handle the load that a HotPlate will, but should be good for 15-20w or so. I'm using a Radio Shack L-pad and the voice coil/magnet assembly from a speaker that developed voice coil rub. We'll see what transpires.
Anyways, THD stuff is built great and love the Twain/Banzai quotes!
I don't remember who, but someone was supposedly putting something like "This Amp was built using 100% Alimony" on their boards.
Edit: @CJ after further thinking, I seem to recall the 2nd lamp was part of the power soak/hot plate circuit.
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frans
Well-known member
It is a nice and versatile little amp. I also got the hot plate and i'd say the hot plate sounds nicer than the built in kinda-hotplate.
The lamp on the hot plate is part of the "noise reduction" - if you don't shave off more than 8 dB max it sounds fine, beyond that it changes too much for my taste.
The lamp on the hot plate is part of the "noise reduction" - if you don't shave off more than 8 dB max it sounds fine, beyond that it changes too much for my taste.
amplexus
Well-known member
I remember when these series came out and they were all the 'rage' so to speak. Always liked the sound of em tho! I built an AX-84 way back in the day using a KT88 and it definitely was loud enough!
Yes looks like the lightbulb is spliced on to the wire wound power soak,
This thing runs at about 500 volts B+ supply with the HV switched, a bit much for a self bias amp, I am going to tell he customer to run it with the switch in the LV position which drops it down to about 360 since the reason it came into the shop is a blown KT 88.
Looks like a Bax/James tone stack after a cathode follower, with some NFB going on,
This thing runs at about 500 volts B+ supply with the HV switched, a bit much for a self bias amp, I am going to tell he customer to run it with the switch in the LV position which drops it down to about 360 since the reason it came into the shop is a blown KT 88.
Looks like a Bax/James tone stack after a cathode follower, with some NFB going on,
