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Anybody built a Matchless Hotbox?

4/14/2000 1:11 PM
Eric H
Anybody built a Matchless Hotbox?
Just thought Steve A's and Aron's post was a good one, and I'd like to know also.  
4/14/2000 11:03 PM

Building one right now along with the vibrobox. Got the PS up and running, circuit doesn't blow anything up yet, still working on the relay switches. I also have some ideas for a few mods, after it's running I may try.
4/15/2000 3:01 AM
Eric H

Great, I'm very interested in how the vibrobox turns out also (probably need vibrato more than another overdrive!).  
4/15/2000 7:32 AM
Steve A.

    Keep us posted on any errors you may find, or improvements that you make to the design. Along with the source for the PT you used, etc.  
    Eric- the Hot Box is not just an overdrive, but an alternate/auxilliary all-tube preamp... The stock "Clean" channel on it is not supposed to be that great hence the idea of wiring up the VibroBox as the second channel for the HotBox. (With the tremelo switched off, the VibroBox is supposed to get some really great lower gain sounds- much better than the Clean channel of the Hot Box... or so I've heard.) So many projects, so little time!  
Steve Ahola
4/17/2000 5:28 PM

Hey, Steve and folks:  
I set this up using the Vibrobox as "clean" and vibrato, and the hotbox section is on complete bypass; this way, I can "tune" the hotbox section in case I get any nasty oscillations (I hope!). As to the PT, I used one cannibalized out of an old Lafayette radio, it puts out way too much voltage, but I knocked it down to about 270V when it hits the circuit. The chassis is an old Legend amp chassis with a lot of room in it for keeping the parts separated (once again, I hope!). The heaters are running off of 6.1-6.2 Vdc, and I'm running the switches with reed relays.  
I still have yet to plug it in, I need to finish the relay section. One thing I did, was on the first stage cathode bypass, I used a Polyester 2.2 mF cap instead of an electrolytic (big as a "C" battery, but I'll make it fit). And, I won't be using the "clean" channel on the hotbox section at all, see above. I figured why have 2 clean options, when 1 of them may compromise the OD sound.  
Any suggestions, advice, comments welcomed heartily!  
4/17/2000 10:04 AM

I'm building one right now. I had some heater hum, did get rid of it by rectifi the 6,3 voltage. Now my problem is that when I goe over 60% on the gain it starts to oscilate, I have reduce the oscilation by rearrange the plateresitor, but still I can't goe over 60%. To night I will try to lower the plate resitor on gainstage one and two from 220K to 100K. I have lowerd the plate voltage from 280V to 245 but still it oscilate. The sound from the clean channel is little to bright for me, I will have it to sound transparant but with more volume. Channel 2 sounds pretty good.  
4/17/2000 1:55 PM
Eric H

Lars, someone else told me the clean channel isn't too good. The cathode-bypass cap on the first-stage is pretty small, but making it larger may give tooo much bass for the overdrive section. The 180pf and 500pf caps at the clean volume could probably be reduced to reduce brightness --it probably needs a tone-stack there too. Maybe remove those two caps and the 220k resistor, and add a 2-band tone stack, this might cut too much gain from the clean channel, though. I'm not good at gain calculations.  
I can't be of much help with the oscillation.  
I assume you've tried some of the simple fixes: poking wires around with a wood stick, input leads near output, etc.  
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