Baldwin 46H Stereo Amplifiers
My fellow sonic explorer, Jason, gave me four Baldwin 46H’s with one goal: Build working amps from what I had.
Nearly stock Baldwins, only the power supply had been redone at this point.
Initially, we planned on 2x super interesting triamp setups for custom speakers, and we’d both walk away with two killer monoblocks. Unfortunately though, I discovered one of the amps had been severely blown up and had a totally different power transformer. So the idea of four identical amps went out the window. I realized that I could build myself a 2x’40w’ amplifier with the parts as I had, as the OT was still fine from the blown amp. I sent the pic below to Jason and he called me immediately and said “build me one of those too!” So I got to work.
I found and bought a Baldwin 46H schematic online, as Jason and I decided to leave the design original to the ‘40w’ channel, but make it twice. It’s a nice little sandbox for modifications. I didn’t need to do any calculations for power as we’re actually running one tube short of the stock configuration, so I was certain the power supply would be able to support the new design. I then made a schematic to refer to as I built the amps:
Rewiring the amps:
Installed the second output transformer and began wiring up heaters and ground.
More work on the second amp. Upped the wattage of the 100ohm power supply resistor.
Each amp in the final stages of wiring. At this point, I ordered custom designed input and output plates.
The custom input/output plates fit perfect. The switch near the volume controls was originally an NFB switch that we removed from the final design, so feel free to ignore it.
Chokes finally installed (TIGHT FIT), input/output plates installed. One amp has WIMA .1’s, the other (mine) has KY409-Y .022’s in the signal path. I’ve spent time listening to both, and the .1’s have significantly better bass response. I’m going to maybe buy some fancy .1uf caps from Sonic Craft to see how it sounds.
Done!
We are all wrapped! The amplifiers each measure 24.5WPC before clipping which is interesting as these are labeled as being able to deliver 80 watts between 3 channels, I figured it’d be closer to 30WPC. It didn’t really make sense from the start as there’s no way 4x 6bq5’s could deliver 40W in this configuration.
The plate voltages are incredibly high with the local AC coming out of the wall, (+354VDC at first node) so I’m using 6P14P’s instead of 6BQ5’s.
I gave mine to my Dad. Here’s his basement setup. U-Turn Orbit, Pioneer SC-70 Preamp, Baldwin 46H Stereo Amplifier, JBL L56.
The frequency response is about what I expect from a nearly stock organ amplifier, the -3db cuttof is around 20khz.
Nice low-end performance, only down -1/2 db @ 20hz. Dad’s reggae slams!
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