|sorin65||3/7/2018 3:20 PM|
|weird component in Magnatone 260A|
I'm looking to restore an old 50s era Magnatone 260. I found some weird components, never seen before. please help identify them- in the schematic are between anode and cathode for the second triode for each 6CG7 tubes. in the pictures is about the square plastics with colored dots. any clue? thabks!
|dstrat||3/7/2018 3:26 PM|
|Probably the 820MMF|
|Bloomfield||3/7/2018 3:56 PM|
|Look up 'domino' capacitors and you'll find a guide to the colour codes.|
Here's one: http://www.radioremembered.org/capcode.htm
|Steve A.||3/7/2018 5:27 PM|
I've been reading about Magnatone amps for 20+ years but never realized that they were point-to-point and looked like THAT!
|Enzo||3/7/2018 5:34 PM|
|Looks like the insides of any TV, radio, hifi, of the 1950s and 1960s.|
When you don't know what a part is, and you already have the schematic, then just look where the part is wired to.
I would agree they are the 820pf from the schematic, plus the color code on the part says 820.
I have to admit I have never seen caps held down with big washers like that before.
|sorin65||3/7/2018 6:47 PM|
|thanks for the answers, but I make a mistake... the components that I don't know what are, are the two brown "tubes" that goes from the 820pF capacitors to the cathode and anode of each second triode of 6CG7. even on schematics looks weird. take a look! also I measured each one, are not resistor, are not capacitor,look as open circuit.[ATTACH=CONFIG]47461[/ATTACH]|
|Tom Phillips||3/7/2018 6:50 PM|
|Those are varistors. Part of the unique Magnatone vibrato circuit. Be very careful with them. They are hard to find and expensive when you can find them.|
|52 Bill||3/7/2018 6:54 PM|
I see that Tom has answered already.
|soundmasterg||3/9/2018 10:59 AM|
|Mick Bailey||3/11/2018 5:52 AM|
|Out of interest, has anyone here built a Magnatone-style amp with the vibrato circuit, and maybe using a replacement for the original varistors using MOVs and resistors?|
|Steve A.||3/11/2018 6:17 AM|
|soundmasterg||3/12/2018 11:02 AM|
|trobbins||3/12/2018 9:55 PM|
Note that it is difficult to check/measure their operation, and they typically never fail, so if there is a problem with your vibrato then don't assume it is the varistors (leave them well alone).
|trobbins||3/13/2018 3:23 AM|
|Article on those varistors:|
|nickb||3/13/2018 4:18 AM|
|trobbins||3/13/2018 4:52 AM|
|Ta - I certainly enjoyed collating the historical aspects. I did most of that a few years ago, but as they are living docs they get a new date if I add anything - which was related to chit-chat over xmas with a crowd cloning the circuit in solid-state (a bit more 'pedal' friendly than a batch of tubes). Next thing you know they'll have a software plug-in for a Rasberry pi.|
|Mick Bailey||3/13/2018 5:29 AM|
|That's a really nice piece of work and very readable. I think I'll include vibrato in my next build as it will add a lot more interest. Just a few projects to finish off in the meantime.|
|bob p||3/13/2018 5:56 AM|
Today people use hot melt glue and silicone RTV to accomplish the same results.
|bob p||3/13/2018 5:59 AM|
|Sorin65, I'd appreciate it if you could post extensive photo documentation of the inside of that original Magnatone. I love looking at old PTP wiring techniques and I think there'd be general interest in a well-documented Magnatone interior.|
|soundmasterg||3/13/2018 10:41 AM|
|Mick Bailey||3/14/2018 4:08 AM|
|I think its really important to get original amps fully documented. Things get changed, amps get re-capped and as we move on we need to be able to look back and see how it was done then. I'm referring to 'we' as people interested in vintage amps. Probably no-one else is interested. I'm fascinated by the build processes, techniques and components used in old electronic equipment.|
|soundmasterg||3/15/2018 5:14 PM|
|Sorry for the delay...got busy with other things. Here are some pics I have of a Magnatone 260A bob p.|
|sorin65||3/16/2018 8:32 AM|
|thanks all for answers and comments!|
I repaired the Magnatone and sounds very nice.
hope you'll like:
|bob p||3/16/2018 10:20 AM|
|So tell us what was wrong with it.|