Poor Man's 5E3 - Help Stop the Pop

[Boots Deville]

I had a spare Weber reverb unit PT, 260V non-CT secondary, 100mA that I thought I'd use in a budget 5E3 head build.  I've built a couple 5E3's in the past, but both have found their way to new owners, and I miss having one around.

So here is my poor-man's 5E3(ish) amp:
Changes include:
- SS Rectifier
- .02 Coupling Caps in the preamp
- .05 Coupling Caps from the PI
- 1M Grid Stopper to the Cathodyne
- 22K Grid Stopper to triode before the Cathodyne
- 470R Screen Resistors
- Second dropping resistor in the power supply dropped from 22K to 10K to account for lower B+
- Single input jack with toggles to select Bright/Normal/Bridged input.

I used one of these PTs in a 6BM8 amp and got almost 360V B+, but in this amp I got a B+ of 340V and 328V on the 6V6 Plates.

I'm *really* happy with the way it turned out.  For obvious reasons, I thought there might be noise issues.  When I first powered it up, I had the red secondary wires running over the board to the rectifier diodes, and I had more hum than I would have liked.  The hum level changed with volume/tone settings.  Chop sticking indicated that moving those secondary wires away from the tone pot decreased the hum.  I re-routed those wires under the turret board and now the hum is all but gone.  Very low noise floor now and it sounds great, even without the 5Y3 sag.  I might be getting some power supply sag.  Sounds great to me.

One issue I'd like some input on.  Instead of the four input jacks normally found on a Tweed Deluxe, I only included one, and added to toggles to be able to select between Bright Chanel, Normal Channel or Bridged (both channels).  These work great, except there is a pop when switching either one.  I've attached the schematic for this.  Any ideas where I might strap a 10M resistor or two to stop the pop?

[jjasilli]

1M or 10M resistor goes across ea pair of SW lugs:  with the SW ON, the resistor is shorted and signal passes through the SW terminals around the resistor.  With the SW OFF, the resistor is technically making a connection, but it's high value fully attenuates signal.  This is often good enough to kill SW pop.

[Boots Deville]

Thanks.  So you're saying with a DPDT and a SPDT I'd need six of these resistors.  Being mini-toggles with tiny lugs and without much real estate, I was hoping to strategically reduce this number, but maybe there isn't a way.

[Willabe]

I think he means 2 for the DPDT and 1 for the SPST.

Real nice looking build!


                      Brad     

[jjasilli]

I think that's a SPDT SW.  Let's work on that SW first. Maybe try a R across the bright & normal lugs.  If that doesn't kill pop, or leaks signal; then try 2 R's: one R from Bright Lug > Center Lug; other R from Normal Lug > Center Lug.

[Boots Deville]

I think that's a SPDT SW.  Let's work on that SW first. Maybe try a R across the bright & normal lugs.  If that doesn't kill pop, or leaks signal; then try 2 R's: one R from Bright Lug > Center Lug; other R from Normal Lug > Center Lug.

Thanks, but I'm a little unclear.  The SPDT switch is the Single/Bridged switch, not the Bright/Normal switch.  But I'll try that on the Single/Bridged switch - large resister across the outside lugs.  If that doesn't do it, two resistors connected to the center lug, one to each outside lug. 

She's in the cab right now for a gig tonight, but tomorrow I'll get her back on the bench.

Cheers!

-John

[LooseChange]

Cute little amp!
I think if you just add a 1m to each grid to ground you will be good to go.

[Boots Deville]

Cute little amp!
I think if you just add a 1m to each grid to ground you will be good to go.

Thanks Dan.  I tried clipping in a 10M from grid to ground, but that didn't do the trick.  And I also only did one grid at a time "just to see...".  Maybe the one left floating was still causing the pop.  I'll try that with 1M on both grids.

[jjasilli]

Yes, sorry, I meant the Single/Bridged SW.

[kagliostro]

Very nice job

Look here how Vox do it in the AC30CC

Kagliostro

[LooseChange]

That's what I'm talkin' about.
Love working on those amps... All those connectors and tracing out the circuit is just so much fun.