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Post subject: Best replacement for Blue Blob Paktron caps
Posted: Thu Apr 04, 2013 12:59 pm
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Roadie
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I have a 71' bandmaster reverb. One of the coupling caps-.1uf/600 second from left-went bad and was replaced with a Sprague 418, not 418p. I have a Jupiter .1/600v hand-rolled mylar/foil cap on hand. Should I replace the 418 with the Jupiter or not? I'd like to keep the other blue blob Paktron. They sound good.


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Thu Apr 04, 2013 2:17 pm
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If the Sprague sounds good, why replace it?

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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Thu Apr 04, 2013 4:10 pm
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If you can get ahold of Bob Rissi of Risson amplifiers he may be able to source you a used but working paktron cap. I was able to get a couple from him. He used to work for Fender and has a few in his surplus.

http://www.rissonamplifiers.com/bob-rissi/

I sourced a few for my '73 bandmaster reverb from him.

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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Fri Apr 05, 2013 9:09 am
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Roadie
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I'm not familiar with the Sprague 418. It's my understanding that the coupling caps should be matched. Everything else in the amp is stock even the electrolytics. I'd like to keep it stock as far as the coupling and signal caps. It sounds OK, but could sound better. Replacing the electrolytics migh help. Thoughts?


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Fri Apr 05, 2013 11:39 am
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Signal and coupling caps are critical to the amp's tone. Filter caps are not. But if you lose one of the latter, you lose the entire amp (at least until repairs can be performed, which may prove to be quite costly). Coupling caps do not need to be "matched" -- merely of the correct value and voltage rating required to perform their task. There's nothing "holy" about the Paktrons IMO -- better to spend money on new Zoso "blue molded" repros if the amp requires replacements.

Arjay

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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Fri Apr 05, 2013 2:40 pm
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Roadie
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Thanks for the feedback. The Zoso's seem to be similar to Jupiters. They look alike and are priced the same. I can tell you from doing a couple of rebuilds with the yellow Jupiters that they sound great in older Fender amps. I bought a 69' Princeton and early 70's Twin cheap because someone had hacked the amps. Between installing Sprague Atoms, Jupiters and tightening the lead dress, both amps sound great. I just picked up the Bandmaster Reverb cheap as well, but it is stock except for the one coupling cap. So this was more of an effort to keep it stock. I'll change out the electrolytics. My kids have been gone all week on Spring break. First time my wife and I have been empty nesters. I could get used to this real quick. :D


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Fri Apr 05, 2013 5:34 pm
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Jupiter Vintage tone and Beeswax caps are really good for vintage Fender amps. And they last a long time. Dynami-caps (red one on the left) are also very nice caps, too. As well metal clad Russian PIO K40Y-9 & K42Y-9.

BTW... old Mallory (brown drops) & Sprague (Mylar) are good for vintage tone, too.

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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Tue Jul 02, 2013 2:00 pm
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Roadie
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This was a basket case when I got her. Total rebuild using Jupiter coupling caps and sprague ecaps and filter caps. She sounds better everyday.

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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Sat Jul 27, 2013 1:35 pm
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Roadie
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I bought this 73' Fender Twin for $300 several years ago. It was a mess. Mallory 150's all through, poorly soldered, cheap ecaps. It sounded absolutely horrible. I repalaced all of the coupling caps with Jupiter yellow caps and ecaps with sprague atoms including filter caps. It sound wonderful now. NOS preamp tubes throught as well. Sorry for the poor picture quality.

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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Sat Jul 27, 2013 3:55 pm
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Krankster,

Nice job! I love Jupiter Vintage caps.

BTW... does your Twin have a 5mfd/50VDC bypass cap on V5B (see schematic)? What cap did you use? I've been using the 8mfd/450VDC Atom (see photo above --- it's the long black cap, toward the left of the breadboard).

This cap seems to do ok, in terms of maintaining the original control sensitivity in the Vibrato section.

Thanks!



http://www.webphix.com/schematic%20heav ... strvol.pdf


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Sun Jul 28, 2013 6:50 am
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Roadie
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Thanks. I also replaced all of the resistors with carbon comps save one. It was a bit of work. I use 5uf/150 sprague. Schematic calls for 5/50. So, I bumped it up to 5/150. The higher capacitance, the less vibrato. I dont't think 8uf would make much difference. Here's a link to the schematic.

http://ampwares.com/schematics/100W_Mast_Vol_SF_Twin_Rev.pdf


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Sun Jul 28, 2013 8:45 am
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Roadie
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The twin also had been blackfaced, Mallory 150's throughout, Xixon ecaps and metal film resitors everywhere. It sounded horrible when I got it. The Jupiters are wonderful, but the carbon comps made a huge difference. First thing I did was to change it back to stock. Average rated tubes-Groove Tube 6L6GE-bias around 33ma. The amp sounded better immediately. No offense to anyone, but leave the Silverface circuits alone.


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Tue Oct 08, 2013 1:25 pm
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Krankster wrote:
I bought this 73' Fender Twin for $300 several years ago. It was a mess. Mallory 150's all through, poorly soldered, cheap ecaps. It sounded absolutely horrible. I repalaced all of the coupling caps with Jupiter yellow caps and ecaps with sprague atoms including filter caps. It sound wonderful now. NOS preamp tubes throught as well. Sorry for the poor picture quality.

Image

When I got this amp, the .01 cap (ceramic) and 220k resistor between the right bias cap and feedback cap was not there. The eyelet between the caps that the cap and resistor tie into was never soldered. It's about half way down the the right bias .1 cap and the feedback cap. Can anyone shed some light on this? Is that .01 cap and 220K resistor left out of some 100 watt master volume Twin Reverbs. I followed the schematic and installed the cap (Jupiter Yellow) and 220K resistor. You can see it in the above photo. Thank you, Chris


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Tue Oct 08, 2013 5:39 pm
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Rock Star
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Krankster, those are part of the RC global negative feedback seen in the late silverface era amps. Those with UL taps off the output tranny. See schematic of the 70watt master volume amps:

http://www.webphix.com/schematic%20heav ... tr_rev.pdf


Be sure that the amp has been reverted back to the 45watt master volume circuit, or you run a risk of instability.

http://www.webphix.com/schematic%20heav ... tr_rev.pdf

Main difference is the ultra-linear tap off the output tranny.


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Post subject: Re: Best replacement for Blue Blob Paktron caps
Posted: Tue Oct 08, 2013 6:18 pm
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It's a '71 model, Steve.

The UL series didn't show up until around '76 or '77 (same time as the UL SR -- they share the same chassis).

Arjay

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