Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: sith on January 30, 2019, 03:00:21 pm
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hello guys, I'm starting something like 6v6 superbass clone… in what direction it will develop depends on listening tests during build (i e. will preamp cathode be tied together or separated v1 and v2... prePI MV or PPI frondelli type… fixed bias or cathode etc.).
right now I'm in bit of dilemma about chassis layout, I haven't yet decided if I will house it in separate cab or if I will build it as combo amp… (separate cab in favour of ventilation, vs portability of combo, still I'm a bit reluctant of 'cooking' effect). I'm leaning in favour of 'hiwatt' design vs 'classic' marshall (again, portability - weight distribution, and in combo option I think its perfect orientation because of speaker basket position).
Anyway, a picture says 1000 words, so I made a quick sketch of how I imagine the layout in my head, so… any advice (critic, or sugesstion) is welcome…
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I see you are a symmetrical thinker. Me too! But that's not always a good idea with guitar amps. I highly recommend moving that OT over next to the PT and rotate it 90° with respect to the PT. This keeps leads short to the output tubes and also keeps all the noisy high power stuff away from the sensitive little tubes.
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ye I know that. but that way I'm 'stuck' with building head cab :sad2: still with chassis depth of 21 cm (about 8,5 inches), and if I move input far on right, am I still in danger of making oscillator instead of amp?
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Ampeg B15 had a similar layout back in the '60s. I don't know what the guts look like, but I guess you should be able to do what you want. I'd be interested to follow this project.
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great found it (not sure about forum policies, but in google type ampeg B15 inside' and load of pictures came up)... definetly interesting. Oh well atleast I'll be forced to drill some more holes if things went south… Tnx Sluckey, and no worries, I'll keep in touch ;)
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is the "example" a steel box with steel boxes covering the trannies, might make a difference from open tranny on AL
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shooter, it's steel (cort mx30 is donor actually :icon_biggrin:), actually I was more considered about hi voltage leads crossing with signal wires
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some more updates… schematics for fixed bias, cathode bias and frondelli master volume… I'm planning on SS rectification with sag resistor… I didn't put any values of PS resistors till I finish it …
Also as for the fixed bias version I simply have copied Mark Huss's bias circuit, so can someone please confirm me values, my PT is 270-0-270, do I need to adjust it, or is it ok as-is...
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I like to use a 50K bias pot in that circuit.
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Sluckey, like on your version of plexi? Then should I change those 47u caps too? Also can 100k pot be used instead 50k pot and 47k resisitor? (maybe multiturn pot to avoid 'accidents')
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I used 25µF caps because I had several on hand. If I had had 10s or 47s instead, I would have used those. The value is not very critical in the bias circuit.
DO NOT REPLACE THE 50K POT AND 47K RESISTOR WITH A SINGLE POT! That would allow you to adjust bias to zero volts and that's a bad thing. Tubes will burn up. Maybe OT and PT too.
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:thumbsup: yes I'm aware of that… better safe then sorry :thumbsup:
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Very similar to my recent build. Great amp. I built mine in the Hoffman stout chassis. I used a 50K multi turn bias pot, with external bias check sockets. Classictone Vibrolux style Power Tran. with dedicated bias tap. Classictone Trainwreck style output tran. a/la Germino 35Watt. I'm using a 5U4gb rectifier with about 430 plate volts. Good luck!