another take on a HoSo type amp

[CraigB]

Layout and schematic.  The relay-switched boost with tone control makes it too much fun to play!  Thanks for looking.  CraigB

[goldtop1]

Hello CraigB,
   I am gathering parts for the SH-11 amp build. Your schematic and layout are great but I have one question. The diode on the relay isn't labeled for type. What size and type of diode is this? would a 1N4007 work? Also I'll be using West Labs 15 watt transformer set. Maybe use ToneSlut set in the 56T amp of Tubenit's version of the HoSo 56 amp. This should be a fun build. Did you use star grounding or Buss bar for your ground scheme? Thanks for you time!

                                                Sincerely, Goldtop 1

[CraigB]

Yes a 1N4007 will work fine.  That's what I used.  I use two chassis locations for grounds on all my builds.  Power amp filters, heater center tap, HT center tap, cathode bias resistor and PI circuit/filter grounded at one of the power transformer bolts or cap can grounding tab.  All preamp grounds soldered to a ring terminal and bolted down anywhere in the general vicinity of the input jack side of the chassis.  You'll undoubtedly get higher voltages with the West Labs tranny, but that's OK.  I think around 140, 150v on the 5879 plate is what to shoot for.  Craig

[goldtop1]

Hey Guys I did build this amp with West Labs Transformers. What I would like to do is take out the diode rectifier and install a tube rectifier to maybe lower the voltages and have better options.My question is can I use the heater taps to run the boost switch relay and hook the 6VAC to the new rectifier along with the 275-0-275 ? Or is there an easier way to do this? The amp in question is CraigB's SH-11. The amp really is great sounding! Thanks for the help!

[CraigB]

Whoa!  with that PT and SS rect. you're cranking out way over the 350s on the EL84 plates.  I figured you'd be using a tube rect. with that tranny.  Yes, use a 5Y3 or 5V4 to drop some.  And yes, use the 6.3v filament tap to power the relay circuit.  Sorry for the confusion, but if you look at my schematic, you'll see that my PT is 220-0-220, way lower than the West Labs.

Regards,
Craig

[goldtop1]

Thanks for the quick reply Craig! Actually I have 360 plate voltage. After searching the Hoffman site, I did find a hookup of a relay that showed using the heater taps to power the relay, but I just wanted to be sure.With the voltages I have now I had to raise the 120 OHM power resistor to 200 OHM to get the plate dissipation down to 12. I will install the tube rectifier and regroup! I love the amp, very clean and clear. I play a 1989 Gibson goldtop 1956 reissue with P90's through a 12"red Fang and 12"Hellatone cabinet. Great sound! Craig thanks again for your help!

[goldtop1]

Hello CraigB,
   OK I changed the SS rectifier to a 5AR4, no problem. my question is , do you have a schematic or layout on how to hookup the relay board to the heater taps? do you omit the center tap? how would I do this and still have the center taps for the tube heaters? I am a little confused here.Please help! This is the SH-11 amp.

                                                sincerely Kurt

[CraigB]

Here ya go!

http://www.el34world.com/projects/images/18wattstoutReverbSchematic.gif

You can use your heater center tap in place of the 100 ohm resistors to ground (aka "virtual center tap").  If you were to use a virtual center tap, you would disconnect the heater center tap from ground and cover the end of it with heatshrink tubing.

Bump your dropping resistor value up to 180 ohms as shown in Dougs schematic.

Regards,
Craig