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Post subject: Vibro Champ PT
Posted: Sun Aug 06, 2017 11:02 am
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Roadie
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Joined: Sat Dec 13, 2014 7:34 am
Posts: 245
Here's an interesting VC power transformer. Letters x'ed out and re-stamped and an extra wire. Looks like it's the stock one from '65.

Sure "looks" like a CT for the 6.3v. Rather than using it they may have taped it off on this particular PT and kept the heater wiring "as usual".

UN

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Post subject: Re: Vibro Champ PT
Posted: Sun Aug 13, 2017 8:37 am
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Professional Musician
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I've seen a number of Fenders with the csa test stamp. Not sure what it means.


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Post subject: Re: Vibro Champ PT
Posted: Sun Aug 13, 2017 7:17 pm
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Rock Star
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IIRC "CSA" stamp is an electrical approval board in Canada. Similar to UL in USA. Stamp sign today looks like this.

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https://en.wikipedia.org/wiki/CSA_Group


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Post subject: Re: Vibro Champ PT
Posted: Sun Aug 13, 2017 7:20 pm
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Roadie
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Joined: Sat Dec 13, 2014 7:34 am
Posts: 245
When I get a chance I'm going to check the continuity of the green/white wire with the heater wires. If so I'll check the AC voltage and if it's around 3.15v's, yippy skippy it's a CT.

UN


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Post subject: Re: Vibro Champ PT
Posted: Sun Aug 13, 2017 11:07 pm
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Rock Star
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Interestingly enough, "156P1B" ( the X-out number on your transformer) --- is one of the Fender parts number for the PT CSA designation for the BF and SF era Princeton and PR.

US designation was 125P1B.

Description

Printed on tube chart:
Model “ Princeton Reverb-Amp AA764 ”
Production….#6
Stamped OH (1965)

Components:
Large black transformer stamped 125 P1B with 156 P1B xxxxxx out CSA TEST
Other transformer stamped 125 A10B 606-4-14
Small transformer stamped 125A20B 606-5-26
Cap between transformers marked ASTRON Type EY


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Post subject: Re: Vibro Champ PT
Posted: Wed Aug 16, 2017 8:22 pm
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Roadie
Roadie

Joined: Sat Dec 13, 2014 7:34 am
Posts: 245
The extra wire is a center tap. I get some different voltages with this amp. My heaters are 6.8v's with the original wiring, artificial CT (two 100 ohm) or with the newly discovered CT. With my bias meter the the PV is 358v's with the bias current at 49mv's. I should add that it was the same before and after I changed can and cathode caps. I can get the bias current down easy enough but I think the heaters are a little warm. (Outlets are 124vac)

UN


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Post subject: Re: Vibro Champ PT
Posted: Wed Aug 16, 2017 8:44 pm
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Rock Star
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Rob Robinette's "Bucking Transformer" seem to be a cheap and non-intrusive to the amp, method to reduce outlet power. Here's that link, again.

https://robrobinette.com/5e3_Modificati ... ransformer

This article must have been in the early 2000s. As price for that Hammond transformer is around $25, now. Still, for under $50 in parts, not bad.

BTW... Robinette has some nice sites on gun maintenance and Honda S2000 mods.

:mrgreen:


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Post subject: Re: Vibro Champ PT
Posted: Thu Aug 17, 2017 8:18 pm
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Roadie
Roadie

Joined: Sat Dec 13, 2014 7:34 am
Posts: 245
I'm contemplating adding some extra filtering in this VC by using two 5 watt dropping resistors and the extra 20uf section of the can. (4x20 can) I know the first resistor needs to come off of pin 8 on the rectifier en route to the unused 20uf. The second between two sections and then back to the high voltage/OT. Has anyone used this for hum reduction/lowering the plate voltage?

Thanks for any advice, UN


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Post subject: Re: Vibro Champ PT
Posted: Thu Aug 17, 2017 8:28 pm
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Rock Star
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Eric, many later SF era Champs and the Bronco bridge the first two filter section (in parallel) of a 4 X 20mfd can. To make the first section a total of 40mfd. I haven't really heard too much difference, in terms of hum reduction. You must use a healthy 5Y3GT rectifier, if you do this.

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