Current modifications to a Magnavox 8601-20 SE tube amp for stand alone use. Removal of caps & resistors on inputs to eliminate tone control circuit provided by separate preamp / tuner. Increase bypass cap & 2nd power cap to help bass response.
The first round of refurbishing and testing the AE-3 tube amp is complete. Alterations thus far are:
- Replaced all three 50uf / 25v capacitors with new electrolytics
- Removed R1, R3, and C1
- Installed 1/4″ mono jack in place of phono cartridge input
- Temporary install of IEC power cord (ground is not used yet)
Tested with the trusty Oscar Schmidt OE-30 in case something went horribly wrong, which luckily nothing did. The sound is pretty nice considering the small 4″ speaker (original) used for testing. So far, so good. I’m a little hesitant to tackle swapping out the multi-section electrolytic capacitor just yet as it requires alot of desoldering / soldering. I have no idea what the sound would have been had the resistors and capacitor (R1, R3, C1) not been removed, but because the Kalamazoo schematic did not have them, they were removed. A very mild hum (PS cap?), but I only tested for about 5 minutes. Hopefully, more time tomorrow for further testing. Information for various Kalamazoo mods which should / could be applied: Kalamazoo Mods.
After doing some research on the Talking Book AE-3 circuit, it appears to bears a striking resemblance to the Gibson Kalamazoo Model 1. The Kalamazoo places the volume control with the tone stack between the 12ax7a stages and reduces the overall passive parts count. It also uses the more common 6bq5 as opposed to the 6cm6 in the last stage. For now, it looks like the only major modifications will be the removal of R1, R3, and C1 from the input line. I have also decided to replace the multi-section power capacitor with a similar new-old-stock Cornell Dubilier 40-40-10 @ 450V purchased on Ebay for $35, as well as ordering three 50mfd/50v axial electrolytic caps from Angela Instruments for $12. The dinky 4″ speaker will be replaced after the amp goes live and is tested.