Friday, May 8, 2015

National Model 22 Amplifier. RARE AND AWESOME!



This is a truly rare gem, a mid 60's National Model 22. This one wins the "I want one" award of the last 15 years. It's a whopping 5 watts with RIDICULOUS reverb and tremolo. I mean, Fender did a nice refined job with their reverb but other manufacturers such as Valco (this is associated with them) made that Wild Man reverb that I prefer.

This amp was sick when it was brought to me. Noisy, volume dropouts, tremolo caused this horrific noise through the speaker.

First thing to address was the obvious. It spent time in a barn. It needed major cleaning. Pots, jacks, sockets, tolex, the works! Next the power supply caps were toast. One had burst. Easy fix. I noticed the 330 ohm 3 watt cathode resistor on the 6V6 output tube broke in half. So I replaced that with a 10 watter. It will never die again. Then the tricky part: the tremolo. BUH BUH BUH BUH THUMP THUMP CRACK CRACK CRAAAAACK.... There are no schematics I could find for these but other National amps are close enough. I found a Gretsch that was really similar, single ended class A 6V6 loaded amp with reverb and tremolo. But if you can't find a schematic let your experience find the circuit:


Yes, these amps have the 'bowl o' Pad Thai' hand wired circuit. I know this pic sucks but can you find the tremolo circuit? I can!
When you see 3 caps in series like this with one going to ground you most likely found the tremolo circuit. I replaced the old 220k load resistor since it was way out of tolerance. I also added a 100 ohm buffer resistor between the tremolo output and the tube it feeds into. This amp lacks an 'intensity' control. This helped but the real cause was much sadder....


This amp has it's original Jensen speaker. Sad to say, this was the cause of much bad distortion and the tremolo nonsense. The voice coil was starting to separate. Too bad. Worthy of a re-cone but we're just going to drop in a replacement today....


I like these Mojo Speakers. They sound nice and are affordable. 25 Watts. The original was ceramic so this makes life easy.

Also added a line out off the speaker. Plugged into my amp it just sounds huge at any volume. Really warm and friendly. You want to never stop playing.

One other little thing I did: the cap after the first preamp stage was a .005. I upped that to a .022 for a fuller bodied tone. For a 5 watt amp this baby has nice low end.

All the tubes are good, nice old American glass. None finer!

How does this amp sound???????????? All I can say is wow. Surf is most definitely up! Reverb has that characteristic buzz but so what?! When you are blasting it's not an issue. It really has a punch to it with my trusty '58 Jazzmaster. Yeah, I'd play jazz through this. Cowboy music too. Psychedelic! I WANT ONE! It's not common to see a 5 watt amp with a 12" speaker, great combo that holds together better than one would think. I'll be sad to see this go. In the meantime I may just have to record with it......



JB

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