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Topic: Sho Bud Compactra 100 service? |
Jim Rossen
From:
Iowa, USA
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Posted 25 Feb 2022 11:20 am |
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Looking someone to service a complete but nonfunctional Sho Bud Compactra 100 tube amp. I favor someone with previous experience with this particular amp as the build is congested.
Thanks
Jim |
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Michael Brebes
From:
Northridge CA
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Posted 26 Feb 2022 9:21 am
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I have the schematic and the amp looks very straight forward in design, with lot taken from standard Fender tube amp designs. I am in California.
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Michael Brebes
Instrument/amp/ pickup repair
MSA D10 Classic/Rickenbacher B6/
Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso
Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100 |
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Jim Rossen
From:
Iowa, USA
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Posted 26 Feb 2022 9:46 am
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Jim Rossen
From:
Iowa, USA
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J Fletcher
From:
London,Ont,Canada
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Posted 27 Feb 2022 2:20 pm
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| Looks to me like the 6SC7 is dedicated to the reverb drive circuit , and the dry signal should be unaffected by the 6SC7's omission . Don't see why any competent amp tech couldn't sort this amp out . |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Mar 2022 1:39 pm
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 Here is a complete Compactra 100 schematic. Scanned into PDF by Jim Evans and sent to me around ten years ago. The above schematic is cut off on the right side
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Ken Fox
From:
Nashville GA USA
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Posted 3 Mar 2022 1:46 pm Telestar
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The original amp was built for Albert Talley. It was called a Telestar. Only difference was the Compactra had a sensitivity control in the reverb drive.
Notes from Jim:
When I was adding reverb to the early Evans-Amp in 1961, I had reasons for wanting to get away from cross-coupled-cathodes for recirculation. I was still communicating directly with Hammond engineers, who were giving any help they could to sell their spring reverb units to the guitar-amp market. "Competitors" were trying everything from a rolled 30-foot water hose with acoustical transducers on each end, to electrostatic drums rotating in oil. Up until then, the nearest successful attempt was the two-head tape recorder, pioneered by Les Paul. This was the technology used in Gibson's "Echoplex". This tape method had the problem of giving a diminishing-echo-repeat, rather than a steady concert-hall decay.
I way trying numerous techniques when one morning about 1:00 AM I awoke, sat up in bed, and startled my wife by saying "Ive got it!". She thought I was having a nightmare and said "Got what? Go back to sleep." I crawled out of bed and answered, "Its OK, you can go on back to sleep. I need to go back to the shop for a few minutes". The simplicity had finally hit me, that a simple passive-resistance "H-pad" could send, recover, and remix the direct and the reverb signals, without cathode-coupling. In about ten minutes, I had the circuit working on the bench, and went back to bed.
The next morning I awoke about 6:00 AM. I recall waking up, wondering if maybe I had just just dreamed about working out the problem. Before even starting the coffee pot, I recall slapping cold water on my face, and rushing back to the shop to see how much of it had just been a dream, since often "dreams make things too simple". I opened the shop door, almost surprised to find my breadboard-prototype was really there, waiting to be turned back on and tried again. I recall turning on the amp, plucking some guitar strings, and excitedly realizing that it wasn't a dream. It needed some refinements, but things were now on a roll and started coming together. One was a swamping-resistor in the drive side, to eliminate a "door-spring" sound from the spring-unit. Another was contouring the lows, to reduce the shock-effect, and remove the "gunshot" sound from a stacatto-note. I tweaked the resistance values until it sounded right, and decided to try all this in the first commercial amp I was starting for Albert Talley.
Soon, I had Albert's amp ready for delivery, and already set-up at the auditorium where he was to play with a Western-Swing guest-group the next weekend. It happened that next day downtown, I ran across the Cherokee Cowboys including Buddy Emmons (stopped here overnight for bus repair). We unloaded Buddy's guitar from the bus, took it to the auditorium stage, where he got to try the amp before Albert even saw it. This turned out to be a helpful test for a new amp. In the years to follow, all the Compactra-100 amps I built for Sho-Bud retained this same reverb-circuit circuit setup. |
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Ken Fox
From:
Nashville GA USA
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Posted 4 Mar 2022 5:27 am Amp
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Note that a Fender amp has the main speaker jack grounded until the speaker is plugged in. This protects the output transformer from see a zero load condition
The Compactra does not. Be careful not to work on the amp without a speaker load. That could ruin the output transformer |
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