Posted:
Fri Sep 04, 2009 8:57 amby ChrisK
SteveH wrote:Gents,
What I may do is use a rotary switch to select UL/Pentode/Triode mode in the place of the cap. I believe I would need a 2P3T rotary switch ?
When I tried something similar, I ended up with one pole for each tube. With two KT88's, I used a DPDT switch to switch the resistor and OPT tap for each tube in and out.
Not sure a cheapo rotary switch is suitable for handling high voltage...others would know more about than me. Allied Electronics has a good rotary that might work:
http://www.alliedelec.com/Search/SearchResults.aspx?N=0&Ntk=Primary&Ntt=747-6685, but you'd need 3 positions with 4 poles. They're sealed and rated at 0.3A @ 125VAC. These get kinda 'spensive, though. I'd put some ceramic caps across the contacts also.
Chris
Posted:
Fri Sep 04, 2009 9:01 amby ChrisK
SteveH wrote:Gents,
What I may do is use a rotary switch to select UL/Pentode/Triode mode in the place of the cap. I believe I would need a 2P3T rotary switch ?
Another thought: Use the hole for a regular 8-pin tube socket and plug in a soft-start relay as per Tom's idea. I have a parts reference if anyone needs it.
Chris
Posted:
Fri Sep 04, 2009 9:06 amby ChrisK
TomMcNally wrote:If only Dynaco cages weren't... so... ugly
When original tube amps were invented, they were meant to be tucked in the back and never seen. Hence the industrial look. The preamp was
the front man.
Yeh, amazing how things change. I look at some of the latest Manley amps and I swear they spend more $$$ on appearance and finishing than on components!
I saw another amp somewhere that had the tubes in a freakin' V8 configuration...complete with chrome bars that looked like rollover protection.
Chris
Posted:
Fri Sep 04, 2009 9:38 amby SteveH
ChrisK wrote: but you'd need 3 positions with 4 poles.
Hrmm...As these are monoblocks, wouldn't I just need a 2P3T switch ?
Posted:
Fri Sep 04, 2009 10:29 amby EWBrown
The Manley and VTL (Vacuum Tube Logic) amps use fairly standard "textbook" circuit topology, often with a 12AT7, 6201 or ECC81 as the VA, and 12AT7, 12BH7 or 6350 as the LTPI. Output stages are fixed bias, rather than cathode bias. They tend to run a higher than normal B+ voltage, and somewhat lower plate current.
I've never actually owned a VTL or Manley amp, bit I've been inside several models, and "reverse engineered" their circuitry, which is amazingly similar in all models that I've seen. .
The Poseidon driver board is quite flexible, and with the proper component changes can be used to drive about any PP output stage.
/ed B in NC
Posted:
Fri Sep 04, 2009 1:11 pmby ChrisK
SteveH wrote:ChrisK wrote: but you'd need 3 positions with 4 poles.
Hrmm...As these are monoblocks, wouldn't I just need a 2P3T switch ?
You're absolutely right. I was thinking of my own scenario where I'm building two Mark III's in one chassis.
Chris
Posted:
Mon Sep 21, 2009 11:08 amby SteveH
Here's the finished product:
