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Post subject: Re: 1971 Super Reverb
Posted: Wed Aug 16, 2017 3:14 pm
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Location: Coastal Bend, Tx.
Quote:
Try to keep the 220k-ohm G2G resistors in your circuit. And use good ones. 5% or better tolerance. I even check two resistors side-by-side, in the DVM to match the best pair.
All 16 replaced resistors were upgraded to 1% and matched as closely as possible within each section. Cant avoid completely some minor shifting due to solder application, some spots are just really tight/awkward and occasionally a re-flow is required. Even w/ heat sinks, when the leads are really short the heat/contact time is to much. But still talking about miniscule numbers in most cases or a replacement is dropped in.

Yeah, $70 for a pair of gz34s from the mid eighties is a great bargain vs modern production. Although, I have over 5 years on a JJ in my DRRI w/o a hitch so they do the job as well.
I don't have enough experience to say whether old vs new is a legitimate reason to spend over $100 for a NOS recto tube. I wouldn't disagree with either arguments points, but would say for certain that different tubes produce different results. I bought a pair of MIJ Amperex that I will try in the SR and the DRRI so I will have my first comparison between old/new. Looking forward to comparing them, I don't think it will be as big a difference as the 5y3 to 5v4 in the Bronco was.


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Post subject: Re: 1971 Super Reverb
Posted: Fri Aug 18, 2017 6:31 pm
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Finally got off my butt and soldered the bias & bias-balance. 1st swapped the resistor in the bias supply back to AB spec 470ohm 1 watt.
Image
Image
Tested the circuit unloaded and both pots functioned as expected.
Set the unloaded bias at -52.25vdc for a starting point.
Waiting on a couple tubes from eBay:
Image


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Post subject: Re: 1971 Super Reverb
Posted: Fri Aug 18, 2017 6:43 pm
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In my experience, I had issues with OEM Russian and Chinese 5AR4. Primarily in 1980-90s era amps. I scooped up a bunch of Mullard and Philips GZ34, GE and Sylvania 5AR4, at the time. All NOS. I have not heard of any problems with amps that I used these rectifiers (I always upgraded filter caps and usually PSU rail resistors in these amps I fixed). Except for a couple whose rectifier got weak over the 20 years of gigging. But, no fireworks and popped caps --- even in heavily used and abused units.

I have not heard of arcing or other premature issues with these R&R amps. And this includes a couple hi-fi amps that are notoriously hard on rectifiers (like the Dynaco ST-70 and ST-120).

This is just my experience. And I've heard that newer made Russian and selected Chinese made 5AR4 are much better. I have not tried these.

BTW... in many cases (esp hi-fi). It's better to modified the PSU to full solid state. I prefer UF 5408 sextet diodes. Current rush limiter help excessive current rush into the filter caps. All amps above 40 watts should have ss rectification, IMHO. Much more reliable, over the long haul. Esp if you operate the amp is in constant use.

:mrgreen:


Last edited by BMW2002Ti on Fri Aug 18, 2017 6:55 pm, edited 2 times in total.

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Post subject: Re: 1971 Super Reverb
Posted: Fri Aug 18, 2017 6:51 pm
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If those GZ34/5AR4 rectifiers have cross-hatched seams at the top of the tube (one heavy, the other could be very light) --- they are Matsushita made tubes. Prolly late 1960-70s. These are EXCELLENT tubes. Made from Mullard-Philips dies and assembly jigs sold to Matsushita, as the Euros were phasing out GZ34 production. Built to same tolerance standards as the Dutch and Brits.

Matsushita US named products is Panasonic.

Image


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Post subject: Re: 1971 Super Reverb
Posted: Fri Aug 18, 2017 8:36 pm
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I was thinking initially that the 1st three numbers of the box code may be the date 3-70.
Was aware of the Matsushita cross hatch tops, have a handful of pre-amp tubes from them.
Might be here w/ Sat. mail, that's all I'm waiting on. Was thinking about just going w/ a 5u4gb for a 1st run-up but after finally finding a good pair of gz34 at a fair price, I'll just wait. But if they don't make it here on Sat. I'll likely pull the JJ from the DRRI for the 1st start-up.

Appreciate the comments on the older rectifiers(I'm keeping my eyes open for others, unfortunately those Phillips pairs got away) and the point about SS being the prudent path for bigger rigs that get gigged a lot.

As far as diodes go, I'm illiterate. I know I haven't seen the 1n4007 listed new anywhere. I've only seen 1n4006, is that the common replacement or should I be looking at some other designations. You mentioned the UF5408, would that be a replacement also for the 1n4007 or only for the replacement of rectifiers?


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Post subject: Re: 1971 Super Reverb
Posted: Sat Aug 19, 2017 2:35 am
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sfceric64 wrote:

As far as diodes go, I'm illiterate. I know I haven't seen the 1n4007 listed new anywhere. I've only seen 1n4006, is that the common replacement or should I be looking at some other designations. You mentioned the UF5408, would that be a replacement also for the 1n4007 or only for the replacement of rectifiers?


I would buy UF-series diodes. These are ultra-fast, quieter, and cost about the same.

The 1N4006 handles lower PIV voltage at same current than the 1N4007 (800PIV versus 1000PIV). Once again, buy UF4007.

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

The UF5408 has a much greater current flow at similar voltage to the UF4007. I like replacing main power solid-state diodes in Twin Reverb, Bassman, and Showman amps with these diodes.

Image

https://www.microsemi.com/document-port ... 6-lds-0211

I like the UF4007, in the bias supply.

Cost of UF diodes:

http://www.mouser.com/ProductDetail/Fai ... LMBA%3D%3D

http://www.mouser.com/ProductDetail/Vis ... EsjIvZoKD4


Last edited by BMW2002Ti on Sat Aug 19, 2017 6:59 am, edited 1 time in total.

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Post subject: Re: 1971 Super Reverb
Posted: Sat Aug 19, 2017 6:26 am
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Thanks for the links and info.

Edit:
The MIJ Amperex 5ar4/GZ34 pair showed up in the mail today, they are dated from 83 but are still nicely cross hatched Matsushita but I am to tired to do anything with them today.


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Post subject: Re: 1971 Super Reverb
Posted: Wed Aug 23, 2017 5:44 pm
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Still haven't finished,
mom was in the hospital again (Sun-Tues) and now Harvey is potentially gonna keep me from any hobby activity...Blah, had to go up in the attic this morning to fetch window coverings and then a quick property sweep for loose impediments.

Nice little 1958 Gretsch 5 watter on eBay looks interesting, for repair/not working.
Picked up a few Amperex el34's from the early 80's as a substitution from a deal I did on eBay recently.
I don't have a need for currently but may buy a little T50 Infidium since I don't own a higher gain amp.


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Post subject: Re: 1971 Super Reverb
Posted: Wed Aug 23, 2017 10:08 pm
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Hope your Mom gets better, soon.

Have the link to that 5-watt amp? Sounds interesting.

:)


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Post subject: Re: 1971 Super Reverb
Posted: Thu Aug 24, 2017 6:40 am
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Thanks,
Here's the link:
http://www.ebay.com/itm/Vintage-Gretsch-Amplifier-550-10-Speaker/172828914230?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1431.l2649


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Post subject: Re: 1971 Super Reverb
Posted: Tue Aug 29, 2017 3:14 pm
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Well I just made it back to Corpus Christi this afternoon. Blessed and very lucky Harvey didn't hit the city directly. Lot of people/places still endured the tragic consequences of its destruction.
May have to head to Houston once the waters recede to help family/friends.
The super reverb can wait.


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Post subject: Re: 1971 Super Reverb
Posted: Mon Nov 13, 2017 5:39 pm
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Well I'm bout to get back to fixing this amp. Ya I know it shoulda been done already.

I got a little cabinet repair to do and associated Tolex repair. Its not like I have a wood shop or anything but they don't sell the same stock as they used to and I'm replacing a single 3/4" piece from a 1" stock.
Then I have to remount the reverb tank and replace a few bright parts.
The chassis is almost ready to go, I just need to review all my work notes. I think all is ok and ready to be fired up. Then any components that are outta whack will get replaced.


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Post subject: Re: 1971 Super Reverb
Posted: Mon Nov 13, 2017 7:55 pm
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Good luck, with the final touches.

You have some ceilings and walls that need "dusting-off."

:)


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Post subject: Re: 1971 Super Reverb
Posted: Sat Nov 25, 2017 9:31 pm
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sfceric64 wrote:
Quote:
:wink:I also kept the balance pot, best of both worlds
Thanks for the idea Mud. :mrgreen: I will gladly borrow that. Did you use a 10k or 100-ohm pot, or perhaps an older version? Those seem to be the only sizes available on a quick scan of places I have bought from recently. I'm guessing you ran a separate wiring leg from the bias board to the new pot and left the original pot wired as it was installed.

Got the PB email bomb this afternoon. So I will spend some weekend time to re-locate to a new photo hosting site in an effort to keep the current posts relevant w/ pics.


Sorry I owe you this:
Image
Image
Image
I was in there today, PB sort of changed things for a while
mud


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Post subject: Re: 1971 Super Reverb
Posted: Wed Nov 29, 2017 8:52 am
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Sorry I owe you this:
No problem, PB screwed the pooch for most of its users.
I appreciate the pics, they are a good reference for others as well. The difference is you kept the SF board layout and I switched to the BF layout. In your setup I'm curious as to how/if your add-on bias adjust increases the negative VDC to BF specs. I don't think it can, other than by the range of the pot which may be enough.

Still doing wood work/Tolex and haven't fired mine up yet, may not get to it until after the holidays. My goal is for a New Years midnight blowout!


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