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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 10, 2017 11:35 am
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I certainly wouldn't regard that as beyond the bounds of possibility. If not a fixed-fee deductible then a pro-rated charge based on the unit's age.

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: 1971 Super Reverb
Posted: Mon Jul 10, 2017 11:55 am
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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.


I did use a 10k pot I did tag it right to the balance pot I believe via the resistor that goes to ground after I lifted it, added wire to reach where the polarity switch was, I did have some help, and it was a while ago, and my memory is not as sharp as it use to be. I am away from my super reverb for a little time but as soon as I am back I will take some photos and post them
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Post subject: Re: 1971 Super Reverb
Posted: Mon Jul 10, 2017 8:00 pm
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Quote:
I am away from my super reverb for a little time but as soon as I am back I will take some photos and post them mud
Thanks, that would be great. I think I know how to do it and to be honest I don't think I would tag the other pot unless it is required; but run a stand-alone bias pot w/ separate wires from the bias supply to the new pot and a separate wire run to the board w/ its own resistor.


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Post subject: Re: 1971 Super Reverb
Posted: Wed Jul 12, 2017 12:05 pm
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My resistors and other parts came in yesterday, should be a day or so before I get back to the Super. Decided to push on while the iron was hot and the epoxy on the Bronco was drying.
a few pics, the Bias-Bal Pot and Supply was left alone until later but the circuit board was setup for BF specs, thought that was a good stopping point for the day.
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Post subject: Re: 1971 Super Reverb
Posted: Fri Jul 14, 2017 7:53 pm
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Waiting on a few parts for the bias conversion, they may come in on Saturday.
Update: Parts are here
Well, after all the resistor changes last week I thought I'd put a new tip on the pencil(its a three y/o Craftsman special $9.99) ; needless to say I didn't have a spare nor did Sears and I trashed the old one.
Waiting on a new Weller heater & tips.


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Post subject: Re: 1971 Super Reverb
Posted: Thu Jul 27, 2017 7:04 am
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I'll get back to this as soon as the Bronco Tolex is complete. I think I have all that I need to get it fired up, as long as the tubes that it shipped w/ are good and the diode is ok.


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Post subject: Re: 1971 Super Reverb
Posted: Thu Jul 27, 2017 11:45 am
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Eric,

Just a curiosity question: Why did you choose a 1-watt resistor in the PSU rail after a 1/2-watt one (4700-ohm after the 1K-ohm one)?

Thanks!


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What one of my SR PSU power rails looked like:

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Post subject: Re: 1971 Super Reverb
Posted: Thu Jul 27, 2017 12:10 pm
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Steve,
Its a 1k 3watter followed by a 4.7k 5watter(maybe 7w- looks big to me). They didn't have exactly what I wanted, so I adapted. If you look at the Bronco its the same way except 1k 3w ---> 10k 5w. Ease of shopping would be my only real answer.


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Post subject: Re: 1971 Super Reverb
Posted: Thu Jul 27, 2017 12:55 pm
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Eric, that will be no problems. Now, I put in 2 or 3-watt metal oxide or 5-watt wire wounds in both positions. I like using the bigger MO or WW resistors, in solid-state rectified amps (versus those using tube rectifiers, esp slow-start ones).

:mrgreen:

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Post subject: Re: 1971 Super Reverb
Posted: Sat Aug 05, 2017 2:35 pm
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I've read that wire-wound resistors add some inductance to the circuit Steve, had any issues w/ that?
Finally got back to the SR, this morning. Cleaning up some of the soldering issues I had and building a quick chassis stand. Removed the grounding switch and installed the 2nd 10K-L bias pot in its place. Removed the wiring from the accessory plug and getting ready to re-wire the 3way plug back together.

I'm determined to have both the bias-balance and bias pots. Thinking the best way to get there is to add a separate supply circuit for the BF bias and to leave the balance in place but to re-route the balance directly to the output tubes. Has anyone tried wiring it like this and is it feasible? I'm thinking that allows two separate voltages -44vdc for the balance and -52vdc for the bias. Appreciate any thoughts.


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Post subject: Re: 1971 Super Reverb
Posted: Tue Aug 15, 2017 3:46 am
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Well I've come to my senses and since I switched the tag board to full BF specs, I'll be swapping the old bias-balance pot to a new pot setup as bias only. I am relocating the old balance-pot to the back wall, nearer the output tubes for easier connections directly to pin 1 of each tube. Both pots will work off the same negative supply. Some resistors adjustments will be necessary as @ 121vac from the wall I got -62.2vdc at the diode and slightly less about -56vdc at the balance pot/output tubes. I didn't have the tremolo circuit loaded so that may have a slight voltage draw. I also sourced some 5ar4/gz34 volunteers from eBay, though they were contested by others and should be here towards the end of the week.
To those that may be interested there are currently a couple pairs of those Phillips mis-marked 5v4's listed for a very fair price compared to other 5ar4/gz34's.


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Post subject: Re: 1971 Super Reverb
Posted: Tue Aug 15, 2017 6:23 am
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sfceric64 wrote:
I've read that wire-wound resistors add some inductance to the circuit Steve, had any issues w/ that?

Finally got back to the SR, this morning. Cleaning up some of the soldering issues I had and building a quick chassis stand. Removed the grounding switch and installed the 2nd 10K-L bias pot in its place. Removed the wiring from the accessory plug and getting ready to re-wire the 3way plug back together.

I'm determined to have both the bias-balance and bias pots. Thinking the best way to get there is to add a separate supply circuit for the BF bias and to leave the balance in place but to re-route the balance directly to the output tubes. Has anyone tried wiring it like this and is it feasible? I'm thinking that allows two separate voltages -44vdc for the balance and -52vdc for the bias. Appreciate any thoughts.


Eric, I really haven't had problems using generic "sandbox" brick style wire wound resistors in the power supply. I would not use these in the signal line.

I bought a bunch of non-inductance Mills wire-wound resistors and use them, esp in other ppl's amps. 5 and 12-watt rated ones are about the best WW resistors out there.

http://www.partsconnexion.com/resistors_mills_mra5.html

I have not put a balance and bias pot onto the same amp. It is possible. The BIAS pot must go BEFORE the two legs of C- break off to their respective push-pull pairs (and the BALANCE pot).

You may want to think about a BIAS on the output tubes and a HUM pot added to the heater lines. ALA: '65 Twin Reverb Reissue:

http://ampwares.com/schematics/65_twin_ ... manual.pdf


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Post subject: Re: 1971 Super Reverb
Posted: Tue Aug 15, 2017 6:29 am
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sfceric64 wrote:
Well I've come to my senses and since I switched the tag board to full BF specs, I'll be swapping the old bias-balance pot to a new pot setup as bias only. I am relocating the old balance-pot to the back wall, nearer the output tubes for easier connections directly to pin 1 of each tube. Both pots will work off the same negative supply.

Some resistors adjustments will be necessary as @ 121vac from the wall I got -62.2vdc at the diode and slightly less about -56vdc at the balance pot/output tubes. I didn't have the tremolo circuit loaded so that may have a slight voltage draw. I also sourced some 5ar4/gz34 volunteers from eBay, though they were contested by others

To those that may be interested there are currently a couple pairs of those Phillips mis-marked 5v4's listed for a very fair price compared to other 5ar4/gz34's.


Good to hear more Philips-ECG/Sylvania 5AR4 (labeled as 5V4GA) are available.

You know, you could put two BIAS pots into the bias supply. One for each 6L6GC. Need to put them in parallel from the current branch point of dropping resistor (to ground --- the one soldered onto the pot, itself). Then, break the connection of the two 220K-ohm grid-to-ground resistors (on the 6L6GC grids). Supply each pot to each individual 220k-ohm resistor.

http://ampwares.com/schematics/super_reverb_ab763.pdf

Just a thought...

:mrgreen:


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Post subject: Re: 1971 Super Reverb
Posted: Wed Aug 16, 2017 4:40 am
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Well those two pair of Phillips didn't make it to a bid, they had a buy it now option and went for 69.99 for a pair. A very reasonable price considering what they are.

As far as the bias & bias balance, I'm going to run the BF bias per the AB763 schematic/layout w/o any deviation at -52vdc. And also run a balance pot in parallel w/o going through the 220k resistors off the same negative supply bias voltage but adding the 1069 resistor values to drop the voltage a little, installed at the old polarity switch location. I'll have to run a single supply to the pot from either the bias pot or the supply board and then run a single wire to each output tube. I'll try to preset/test the bias first w/ the balance pot out of circuit, then add an measure to ensure I still have a bias that is within acceptable limits and a balance that functions. The worst that could happen is I fail to achieve a balance function wired this way.

I am dragging my feet on the project though. Haven't touched the chassis in over a week but sometimes its better to digest the plan once or twice before proceeding hastily given my level of experience.


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Post subject: Re: 1971 Super Reverb
Posted: Wed Aug 16, 2017 6:35 am
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$70 per pair, is about as good as I have seen in a few years. There was also an EBay ad for Sylvania (with yellow label) 5AR4, labeled as 5V4GA. I forgot what the BIN price was.

Yes, for BIAS pot you feed adjustable C- voltage to both tubes. With balance, only one tube gets this variable voltage.

The 220k-ohm grid-to-ground resistors (actually grid-to-bias resistors) and part of the tone making of the AB763 circuit. Switching to 100k-ohms G2G in the AA1069 will prolly change the tone. For the worse. 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.

Reverted AB568 to AB763 with one showing 1% tolerance carbon comp resistor (brown 4th band) --- next to green arrow.

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