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I just finished up this kit with a few modifications:
Changed cathode bias resistors to 75 ohm - 10 watt. The EL84s were drawing too much current with the standard 62 and 68 ohm bias resistors. The EL84s are good old stock used tubes.
Transformers built by Bob Wood - Transformer Design and Supply
Rectifier - Weber Copper Cap WGZ34
Changed master volume to the Larmar type. This was a great improvement in tone over the standard crossline master volume. Used a dual ganged 250K pot and bridged the wipers to ground with two 2.2M resistors. I removed the two 220K grid leak resistors.
Changed the channel 2 volume pot to a pot with a push pull spst switch so I could switch the 180 pF bright cap in or out. A 5M resistor is in parallel with the cap to keep it from popping when switched.
Installed a Vari-watt from Skipz circuits. I tried it with the whole amp scaled and also with just the power amp scaled. The unit worked OK with the whole amp scaled, but I had an annoying hum with just the power amp scaled. With the power amp scaled, the preamp power supply is not filtered by the choke. My guess is that the preamp needs to be better filtered. So I rewired it with the whole amp scaled and the hum vanished. On this amp, with all the preamp gain available, the Larmar MV seems to be much more useful than the Vari-watt. Tone-wise, the MV also sounds a lot better.
I was shocked how loud this 30 watt amp can be when cranked up. Fortunately the MV tames it perfectly when needed.
Ceriatone Dizzy 30 - Album - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
Changed cathode bias resistors to 75 ohm - 10 watt. The EL84s were drawing too much current with the standard 62 and 68 ohm bias resistors. The EL84s are good old stock used tubes.
Transformers built by Bob Wood - Transformer Design and Supply
Rectifier - Weber Copper Cap WGZ34
Changed master volume to the Larmar type. This was a great improvement in tone over the standard crossline master volume. Used a dual ganged 250K pot and bridged the wipers to ground with two 2.2M resistors. I removed the two 220K grid leak resistors.
Changed the channel 2 volume pot to a pot with a push pull spst switch so I could switch the 180 pF bright cap in or out. A 5M resistor is in parallel with the cap to keep it from popping when switched.
Installed a Vari-watt from Skipz circuits. I tried it with the whole amp scaled and also with just the power amp scaled. The unit worked OK with the whole amp scaled, but I had an annoying hum with just the power amp scaled. With the power amp scaled, the preamp power supply is not filtered by the choke. My guess is that the preamp needs to be better filtered. So I rewired it with the whole amp scaled and the hum vanished. On this amp, with all the preamp gain available, the Larmar MV seems to be much more useful than the Vari-watt. Tone-wise, the MV also sounds a lot better.
I was shocked how loud this 30 watt amp can be when cranked up. Fortunately the MV tames it perfectly when needed.
Ceriatone Dizzy 30 - Album - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
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