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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Mon Mar 20, 2017 4:23 am
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Thanks once again for all the OUTSTANDING information and advice!

Never having measured tube component voltages I will have some fun getting familiar with it. Do you recommend measuring with the tubes in place so as to complete the circuit, or with the tube removed and measuring at the socket? Have seen information referencing either method.


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Mon Mar 20, 2017 6:57 am
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Tubes in place, no guitar plugged in and the reverb unit not plugged into amp. Controls set to "5." Though this shouldn't be that critical for voltage readings on anodes and cathodes.

DVM set to hundreds of VDC. Black lead clipped to chassis. I like using the small hook probe for the red side. The kind that can hook onto cap & resistor leads.

https://www.amazon.com/Fluke-AC280-Sure ... hook+leads

Voltage on grid side:

Image

Voltage on anode side:

Image


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Mon Mar 20, 2017 7:51 am
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Ah. Much easier than what I was imagining. I sometimes read too much into instructions. Thanks for the pics....and the patience!


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Mon Mar 20, 2017 7:57 am
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Yeah, sometimes it's a bit easier to follow the voltage readings, using the LAYOUT drawing of the circuit --- rather than the SCHEMATIC view.

http://ampwares.com/wp-content/uploads/ ... ematic.pdf


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Mon Mar 20, 2017 6:20 pm
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OK here we go - thanks for the links, voltage measurements are in blue, with some notable or questionable ones (to me) in pink or red:

Everything looked good to me but one anomaly and I don't know if it's normal: The last two on the right (largest) MOLDED blue 0.1uF caps did show voltages well above single-digits but they quickly bled down to zero, and then would never come back up again. Even after waiting for quite some time, and pulling measurements elsewhere. Is that normal, or is that a leaking cap?

Wasn't expecting to see 233 volts in front of the first, small blue MOLDED .01uF cap, noted in red. But neither it nor the 0.6uF blue MOLDED cap had any stray voltage on the other side that bled down .

Image

^^ Hope this isn't an eye chart, just tryin' to be thorough. Thanks for your expertise.


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Mon Mar 20, 2017 7:23 pm
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All caps take time to charge up from cold zero, when they are fully drained of any residual voltage. Cap's DC blocking ability is at operating point, only after being fully charged. The larger the cap's mfd, the longer the charge up time. Time to full charge = (time constant of cap in specific circuit) times (8 to 10). For a 0.1mfd cap = about 1 second, that's it. Any longer is bad.

I'd prolly replace one 0.1mfd cap and re-measure. If it charges up faster than the OEM MOLDED --- replace both 0.1mfd caps. You want close to zero DC on the grid side, ASAP. Those 55-80VDC are going right onto the 7025 (12AX7) signal grid. A grid that are designed to see 1-2VDC max.

The tube's grid maybe getting whacked with every cold start. That's why tube rectifiers or purpose built slow start-up solid-state PSU's are so nice. They keep high DC from the tubes --- until tubes and caps can "warm-up" a bit. But, the Reverb Unit has a solid-state rectifier.

All other voltage readings seem ok. Anode plate and cathode bias voltages. The slightly higher readings are expected, with today's wall outlet voltages. This is good. Those AB resistors are the best things ever made. They really last.

One other thing... the first 40mfd cap in the PSU really takes a beating, esp in this particular 3-diode rectifier arrangement. Replacing this one with a new F&T will prolly help all components downstream of it. Including the other two 40mfd caps. I like ultra-fast diodes, too. UF4007 in place of the OEM 1N4007. Much quieter. Less recovery time issues. Just another FYI...

:lol:

http://www.vishay.com/docs/88755/uf4001.pdf

Anyhow... try the 0.1mfd replacement, get back to us with readings. Good luck! :mrgreen:


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Tue Mar 21, 2017 4:20 am
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Thanks once more for your analysis - will do. I didn't mention that I wasn't measuring DC voltage from power-up, but instead was placing a probe there after power-up (turns out I don't have a clip-style lead). I will measure all from a cold start after work tonight though, and order a couple of 0.1mFd caps anyway figuring worst-case.

I just have to overcome being conflicted about ordering those better-sounding Russian caps you mentioned and putting them in a 'Murcan device that was manufactured during the height of the Cold War. Might as well just toss in some Flouride while I'm at it. Maybe Spragues will be fine for testing...yeah that's it.... ;)

Oh what's the deal with SoZo BlueMolded caps? Not as good?


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Tue Mar 21, 2017 4:48 am
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Stoopy wrote:
Oh what's the deal with SoZo BlueMolded caps? Not as good?


So glad you asked! [Oh no... not another lecture!!!] :lol:

Voicing philosophy of a Reverb Unit (or reverb section of an amp) is different, than the rest of the amp. Those mica caps act to slice off all low-mid to bass frequencies. Check out most Fender amps and you'll see a ceramic disc cap (usually 250-500 pico-farad) feeding signal to the 12AT7 reverb driver tube. Like the Deluxe Reverb:

http://ampwares.com/schematics/deluxe_reverb_ab763.pdf

It's there to let mid-to-high frequencies pass and block mid-to-low. Reverb is primarily the analog-spring delay of high mid-to-high frequencies. Then, adding back non-verbed signal to get an overall spectrum. Mid-to-high frequencies have much more directional quality, than low frequencies. The simulation of music bouncing off walls in a deep hallway is done by delaying these higher signals.

SO... you only need to voice this Unit or section for mid-to-high frequencies. Fancy boutique caps usually get their fame from their reproduction of lower mid to bass. Or the entire frequency range. Polypropylene and mil spec PIO caps have good high end and last. Esp those Orange Drops 716P. This is all you need AND you may find the tone more to your liking versus Jensen PIO, SoZo, or Vintage Jupiter caps. Cleaner vibe with wetter tone.

Worth a try with the OD, first. Save your $$$ for fancy coupling caps, when you redo that tweed Bassman.

:mrgreen:


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Tue Mar 21, 2017 9:46 am
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Well if that's a lecture it's one of the most concise and understandable ones anyone could ask for - I actually followed it, you do a great job explaining this stuff, thanks!

I'll get those Orange Drops and see how one fares - and BTW thanks for the link to that particular vendor, they're within a day's shipping from me.

In the meantime, as regards the PSU, I do have 3 spanking new 40uF 500V Sprague Atoms just sitting in a bag along with a 10K 5W wire-wound resistor that I got just in case the filter caps needed work (stupidly, before I pulled the cover and saw the caps in there now). Instead of ordering and putting in just one F&T cap, wouldn't putting in one (or all 3) Sprague Atoms be just as good?

And I'm hearing that you probably think the 3 diodes in the rectifier circuit could stand to be upgraded with them new super-fast-fangled ones. If that's just as straightforward as any of this other work I'll go ahead and plan to do that - in for a penny, in for a pound at this point, right?

Tweed Bassman.... what I'd give to have my blackface Super Reverb back. Actually a Princeton is what I'd hold out for at this point. :)


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Tue Mar 21, 2017 9:54 am
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Stoopy wrote:
what I'd give to have my blackface Super Reverb back.


+1

I'm down with that. My first new Fender amp was a '67 Silverface Super Reverb -- traded in a '64 Concert Amp and $180 in cash for it. I wish I still had them both!

:lol:

Arjay

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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Tue Mar 21, 2017 10:07 am
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Yup, replace all three PSU caps --- you'll sleep better, for the next 20 years. :)

I replace all diodes of amps that I fix. Of course, I have like 25-50 belt each of UF4007 and UF5408. It's just not worth it having one fail --- they are so cheap. And the Ultra-fast is a definite upgrade. I put a lightweight alligator clip on the body of the diode, while soldering. This keeps too much heat from damaging the unit.

My Reverb Unit with UF4007 diodes.

Image

Sprague Atoms.

Image


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 23, 2017 12:52 pm
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BMW2002Ti wrote:
... Of course, I have like 25-50 belt each of UF4007 and UF5408...


I don't doubt it. It took me a few days to find a place that would sell me just a handful of UF4007's as opposed to a min bulk order qty of 50 or 100. I mean they're cheap enough and all but I don't think I'll find enough homes to give away the other 47 that I wouldn't need.

Well 45 or 46 assuming I roast one or two with the soldering iron... ;)


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 23, 2017 1:53 pm
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Stoopy wrote:
Well 45 or 46 assuming I roast one or two with the soldering iron...


Get yourself a 40-watt Weller soldering station, with a chisel-tip pencil. Will handle most amp and guitar duties with the exception of chassis grounds and attaching the ground wire to a Strat's trem claw.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 23, 2017 4:50 pm
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Retroverbial wrote:
Stoopy wrote:
Well 45 or 46 assuming I roast one or two with the soldering iron...


Get yourself a 40-watt Weller soldering station, with a chisel-tip pencil. Will handle most amp and guitar duties with the exception of chassis grounds and attaching the ground wire to a Strat's trem claw.

Arjay


Thanks Arjay! For once I am actually a step ahead - I have EXACTLY that unit, got it at Sears for a good price. Only downside is they don't carry other tips for Weller but the chisel tip seems to be perfect for this work, and also did well on the circuit board and controls for my Surfy Bear.

Years ago I installed an interrupt switch to my youngest son's Strat (so he could play that BucketHead stuff) and the ground connection was an absolute #%@! with the battery-powered Radio Shack soldering iron I had....

LOVE having a proper soldering station now. Will help when I find that '65 Super Reverb.... :lol:


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 23, 2017 6:24 pm
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Stoopy wrote:
Will help when I find that '65 Super Reverb.... :lol:


Find my '67 silverface too!

:wink:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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