Please help me identify this component...

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Please help me identify this component...

Postby jar240 » Sat Feb 14, 2009 9:14 pm

I've never seen one of these before (let alone all the air-core resistors in this amp). Can anyone identify it and help me to read the code? It's about the size of a piece of Chiclet gum.

Thanks,
Chris

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Postby wyatt » Sat Feb 14, 2009 10:19 pm

Well, that looks very similar to old Silver Mica caps, so called "domino caps," but doesn't look exactly like any one I've seen before.

Someone here probably knows about the color coding.
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Postby Geek » Sun Feb 15, 2009 12:05 am

wyatt wrote:Well, that looks very similar to old Silver Mica caps, so called "domino caps," but doesn't look exactly like any one I've seen before.


Yup! That's a domino SM cap. Got a bucket of 'em. Lovely things for tone stacks and RF.


Someone here probably knows about the color coding.


500pF @ 500V from the looks.

Can some younger eyes confirm?

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby jar240 » Sun Feb 15, 2009 9:31 am

Thanks guys... I was making a schematic for the guitar amp (Beltone AP-50, made in Japan by Teisco) and got stumped here. My capacitance meter told me it was 70nF, but I didn't trust that it was a cap since the meter shows capacitance anytime anywhere, even with the probes disconnected.

Thanks,
Chris
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Postby jonnyeye » Sun Feb 15, 2009 5:09 pm

Yep, 500pf, 500v, 20%. Mica cap color codes are here:
http://www.qsl.net/wa7zcz/area2/page74.html
I have a Beltone AP-14 with (what looks to be) the same tone control in it with a later 500pf cap (it's marked with the value). I'm curious what you think of this type of control - I find that it's very flat in the middle and cuts wildly at the ends, making it fiddly to use. I'm thinking of changing it out.
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Postby jar240 » Sun Feb 15, 2009 7:37 pm

jonnyeye wrote:Yep, 500pf, 500v, 20%.
I learn new stuff every day!

I find the tone control to work as expected, but oddly the overall tone is very dark. I might experiment with some different cap values to get a bit more sparkle. Many of those air-core resistors were noisy, so I decided to completely redo the 6AU6A preamp stage (everything before the vol/tone controls) with this:
http://www.retrodyne1.com/29Wschemo.html

I also redid the heater wiring so that they're balanced using 100-ohm 1W resistors. Big hum reduction there.

I'm generally not a huge distortion guy, but with the preamp change, anything over 25% on the volume level gives me pretty nice sustain...and it's gooooood! It's loud but with a considerably low noise floor when running flat out.

BTW, my first guitar amp was a Beltone AP-12 I got from a cousin...I was only 15 at the time, and foolishly ditched it to get a red-knob Fender "The Twin". Looking back the tone was miles better on the AP-12! I got the AP-50 (Northland 2x12, purple finish) for $220 CAD...

Thanks for the ID on the part and value.

Chris
(Is it REALLY procrastinating if you'd rather tinker with tubes than change poopy diapers?)
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Postby codamedia » Mon Mar 16, 2009 2:07 pm

Jar240,

I have a Purple Beltone AP22 (single 12" speaker) and your thread caught my attention. First, I too was curious about those caps - it was nice to get some answers here! My Beltone also sounds very dark, yet most people that have them find them very bright so I'm not sure what is up there.

Earlier in the thread you mention you were working on a schematic for your Beltone - and later you post scheme for a preamp you plan on re-doing.

I guess my question is - did you ever finish the full schematic for your amp? I'd love to get a look at it if you did!

Sean
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Postby jar240 » Mon Mar 16, 2009 2:45 pm

codamedia wrote:I have a Purple Beltone AP22 (single 12" speaker) and your thread caught my attention. First, I too was curious about those caps - it was nice to get some answers here! My Beltone also sounds very dark, yet most people that have them find them very bright so I'm not sure what is up there.

Maybe component drift... I'm still looking into it, in my spare spare spare time!

codamedia wrote:I guess my question is - did you ever finish the full schematic for your amp? I'd love to get a look at it if you did!

I did finish it, but it looks like crap. I started to use Eagle to make it clearer to read, but I couldn't find transformer symbols. If I rewrite it, I'll post it to schematicheaven or somewhere like that. I made sure to take photos of and make a schematic for the preamp before my modifications, so I have all that.

Chris
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Postby codamedia » Tue Mar 17, 2009 8:06 am

Thanks for the update Chris.
If I solve the high end shortage before you do I'll let you know.
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Postby codamedia » Fri May 08, 2009 2:28 pm

Chris: I just wanted to give you an update from my end.

I did many changes to my AP-22 over the past few weeks including the PT, filter caps, a small handful of resisters and all other caps other than the tone stack. The coupling caps made a huge different in two areas - so I suspect they were pretty much gone. The hum reduced incredibly when I put in new Orange Drops, and at the same time I had a large increase in high end.

I took this little thing to a practise the other night and it was great. 18 watts of tone - and no shortage of high end.

I'd still love to see your schematic if you ever get it done!
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Re: Please help me identify this component...

Postby jar240 » Sat Mar 05, 2016 11:08 am

I just rediscovered this thread of mine, and wanted to post a quick follow-up.

While I abandoned the AP-50 project, the old friend who originally bought my Beltone AP-14 (thought it was an AP-12 originally) called me up to offer it back since he was leaving the country for work.

I gladly took him up on his offer... traded him 6-pack of really good beers for it, so it's now back in the stable. Good tone + sentimental value!
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