Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mars-Hall on April 17, 2020, 05:05:56 pm

Title: 6G3 vs 6G3-A differences?
Post by: Mars-Hall on April 17, 2020, 05:05:56 pm: Does anyone have specifics on the circuit changes Leo implemented?
Title: Re: 6G3 vs 6G3-A differences?
Post by: 66Strat on April 17, 2020, 06:18:04 pm: I don't think that I have ever seen or heard of a Fender 6G3-A circuit. Is this a revision to the Fender 6G3 Deluxe amp circuit that you are referencing?
Title: Re: 6G3 vs 6G3-A differences?
Post by: Mars-Hall on April 17, 2020, 06:34:44 pm: Quote from: 66Strat on April 17, 2020, 06:18:04 pm
I don't think that I have ever seen or heard of a Fender 6G3-A circuit. Is this a revision to the Fender 6G3 Deluxe amp circuit that you are referencing?

Yes, a friend of mine has a brown face Deluxe designated 6G3-A. There isn't any schematics, that I've found, of the 6G3-A Deluxe online. This photo is not my friends amp, found this in my search.
Title: Re: 6G3 vs 6G3-A differences?
Post by: Mars-Hall on April 17, 2020, 08:13:54 pm: shooter, These changes would be equivalent on the 6G3 Deluxe schematic? My amp has the .0001uf cap and the 56k resistor but is designated 6G3 without the "A". Also, what does the A-FB and B-FA designate?
Title: Re: 6G3 vs 6G3-A differences?
Post by: sluckey on April 17, 2020, 08:36:13 pm: Shooter, why do you keep posting about 6G6? The thread is about 6G3.
Title: Re: 6G3 vs 6G3-A differences?
Post by: Willabe on April 17, 2020, 10:35:19 pm: Quote from: sluckey on April 17, 2020, 08:36:13 pm
Shooter, why do you keep posting about 6G6? The thread is about 6G3.

Must be workin' at the bait shop again?
Title: Re: 6G3 vs 6G3-A differences?
Post by: Willabe on April 17, 2020, 10:37:39 pm: It's not in Dave Funks Tube amp book. (A lot of Fender schemos in the back.)
Title: Re: 6G3 vs 6G3-A differences?
Post by: shooter on April 18, 2020, 06:59:10 am: Quote
why do you keep posting about 6G6
cleaned up my poo :laugh:
Dyslexic and tiered eyes :think1:
aside;
had a Physics Prof pull me aside, asked how I could get through complex math, and not be able to add 7 to 8 :help:
Title: Re: 6G3 vs 6G3-A differences?
Post by: Willabe on April 18, 2020, 08:00:14 am: I found this on a Fender Brown Face amp group on face book that I joined a while back.

I also posted a question about if anybody knows about the amp and if there's a schematic for it.

"Deluxe – Never had a 5G3 version. 6G3 schematic in Sept '61. Presumably first units then, as well. 6G3A units (6G3 TCs with "A" inked in) appear in Jan '62, then go back to plain 6G3 TCs in Oct '62. AA763 schematic and units in Sept '63."

(TC = tube chart glued to cab.)
Title: Re: 6G3 vs 6G3-A differences?
Post by: bmccowan on April 18, 2020, 09:06:48 am: I did a search when I built a 6G3. All I ever found was a claim that Fender changed a cathode resistor value in the PI. I thought it rather amusing that that would generate an "A" variation given the many changes that Valco, Magnatone, and Gibson routinely made without ever changing the model numbers. :w2:
Title: Re: 6G3 vs 6G3-A differences?
Post by: shooter on April 18, 2020, 10:18:55 am: Quote
a claim that Fender changed a cathode resistor value in the PI. I thought it rather amusing that that would generate an "A" variation
:laugh:
I was in the right tree, just wrong forest :icon_biggrin:
Title: Re: 6G3 vs 6G3-A differences?
Post by: Mars-Hall on April 18, 2020, 05:26:59 pm: Quote from: bmccowan on April 18, 2020, 09:06:48 am
I did a search when I built a 6G3. All I ever found was a claim that Fender changed a cathode resistor value in the PI. I thought it rather amusing that that would generate an "A" variation given the many changes that Valco, Magnatone, and Gibson routinely made without ever changing the model numbers. :w2:

The cathode resistors are the same values in mine and my friend's amp 56k. :dontknow:
Title: Re: 6G3 vs 6G3-A differences?
Post by: 66Strat on April 18, 2020, 05:47:30 pm: Quote from: Mars-Hall on April 18, 2020, 05:26:59 pm
Quote from: bmccowan on April 18, 2020, 09:06:48 am
I did a search when I built a 6G3. All I ever found was a claim that Fender changed a cathode resistor value in the PI. I thought it rather amusing that that would generate an "A" variation given the many changes that Valco, Magnatone, and Gibson routinely made without ever changing the model numbers. :w2:

The cathode resistors are the same values in mine and my friend's amp 56k. :dontknow:

The only 56K resistor that I see is in the negative feedback circuit. My guess is that Fender may have been experimenting with the PI cathode and tail resistor values. As I said before, I have never seen or heard of a 6G3-A circuit.
Title: Re: 6G3 vs 6G3-A differences?
Post by: bmccowan on April 18, 2020, 06:38:06 pm: Quote
The cathode resistors are the same values in mine and my friend's amp 56k.
When social distancing eases maybe you can open them up and compare the circuits - post the results. Its not a very complex circuit, should be easy to spot the differences.
Title: Re: 6G3 vs 6G3-A differences?
Post by: shooter on April 18, 2020, 06:39:13 pm: Quote
cathode resistors are the same values in mine and my friend's amp 56k

swap hi Rez pics, have a find the difference party :icon_biggrin:
Title: Re: 6G3 vs 6G3-A differences?
Post by: tubeswell on April 18, 2020, 07:28:52 pm: Are you the same OP that was asking on Facebook? Looks like its a temporary transition thing Fender did at some stage early on in the 6G3 production run after they changed the transformers, and then still later on, they just reverted to the '6G3' moniker.
Title: Re: 6G3 vs 6G3-A differences?
Post by: Willabe on April 18, 2020, 11:29:53 pm: Quote from: tubeswell on April 18, 2020, 07:28:52 pm
Are you the same OP that was asking on Facebook?

I asked for him.

Seems like all Fender did was change the PT.

Here's the reply;

"6G3 tube charts with the "A" written in first show up in October, 1961, and ran until about June, 1962. After that, the "A" was left off, and the amps are all "plain old" 6G3s. Note that the 6G3 itself was released the previous month.

I've never found a schematic for a 6G3-A, and suspect that the difference isn't in the circuit, but rather in the parts.

The 6G3 was spec'd to use the 125P2A power transformer. That was soon updated with the 125P17A. The changeover occurred roughly at the same time the "A" was added to the tube chart. I've seen other cases where a change in the transformers prompted an "A" addition to the tube chart model number; I suspect that the version change was used inside the company to inform the assemblers of a change in what they needed to pull from stock, and to let the testers know of a change in voltages."

"If the "A" _is_ related to the transformer change, note that the first 125P17As were ordered in mid-October, 1961, and carry the date code 606-146 (November 12). That lines up with a change in version number.

It looks like there were initially "special" three production runs of the "A" version, in January. In February, the old production numbering sequence returned, though the amps continued to have the "A" mark. The sequence is:

10/61 - Prod 59 - 6G3 - 125P2A
10/61 - Prod 65 - 6G3-A - 125P17A
1/62 - Prod 6 - 6G3-A - 125P17A
1/62 - Prod 7 - 6G3-A - 125P17A
1/62 - Prod 8 - 6G3-A - 125P17A
2/62 - Prod 65 - 6G3-A - 125P17A
2/62 - Prod 66 - 6G3-A - 125P17A
2/62 - Prod 67 - 6G3-A - 125P17A
6/62 - Prod 67 - 6G3-A - 125P17A
9/62 - Prod 68 - 6G3 - 125P17A
10/62 - Prod 69 - 6G3 - 125P17A

So, perhaps by June, everybody in assembly and test was used to the 125P17A change, so the "version" mark wasn't needed any more. The "new normal" had settled in."
Title: Re: 6G3 vs 6G3-A differences?
Post by: Willabe on April 20, 2020, 02:00:23 pm: Where did you go?

I find no mention of a 6G3A in The Soul of Tone, Celebrating 60 Years of Fender Amps.

Dave Funks Tube Amp Workshop has a list in the back of the book that gives most/all Fender amp iron set #'s by amp. It does not have the 6G3A listed, nor the 125P17A code PT listed. It shows the 125P2A for a 6G3, and no other amp is listed to have used either of those 2 PT's.

I did find something on Fender changing the stamped PT code # on a Bassman(?) that at 1st had the old/original # AND the new # stamped right next to the old #. And then just went to the new # by itself. They said that the PT specs were not changed, they just changed the code #. But that was the older tweed number code not the newer 125P _ _ _ _ code system.

Brown Deluxe's show a GZ34/5AR4 rectifier tube. If they went with a 5U4 rectifier tube on the 6G3A's they might have upped the 5acv current from 2A to 3A?

Or they might have upped the B+ high acv current a little bit?

If you can get your friend to see if his PT is stamped 125P17A. If it is, then have him to give you the dimensions, height/width/length, then you can compare them with try and find someone who has a 6G3 Brown Deluxe with a 125P2A.

I'd give Mercury Magnetics a call, if anybody had their hands on a 6G3A 12517A PT and measured it/backwards engineered it, electrical capacity, laments material, physical size , they did. That's what they do. You don't have to buy 1 to find out if and/or what any difference between the 2 might be.
Title: Re: 6G3 vs 6G3-A differences?
Post by: Mars-Hall on April 22, 2020, 04:44:13 am: Willabe, I was satisfied with the explanation you posted from the fb page. It seems to make the most sense.
Title: Re: 6G3 vs 6G3-A differences?
Post by: HotBluePlates on June 14, 2020, 08:53:03 pm: Quote from: Mars-Hall on April 17, 2020, 05:05:56 pm
Does anyone have specifics on the circuit changes Leo implemented?
Quote from: Willabe on April 18, 2020, 11:29:53 pm
... Seems like all Fender did was change the PT.

Here's the reply;

"6G3 tube charts with the "A" written in first show up in October, 1961, and ran until about June, 1962. After that, the "A" was left off, and the amps are all "plain old" 6G3s. Note that the 6G3 itself was released the previous month.

I've never found a schematic for a 6G3-A, and suspect that the difference isn't in the circuit, but rather in the parts.

The 6G3 was spec'd to use the 125P2A power transformer. That was soon updated with the 125P17A. ...

Wow... I never took note of the "A" on the tube chart before!

I used to have a '62 Deluxe and a '63 Deluxe at the same time. I still have the '62 but its tube chart is too worn to get a month of manufacture, but the 125P17A power transformer is from mid-November 1961 and the Oxford speaker is 4th week of January 1962. I saw no circuit differences inside the amps, except for an adjustable bias supply a previous owner added to one of them.
(https://i.imgur.com/YHp3g64.jpg)
(https://i.imgur.com/G25x8XH.jpg)
By the time my '63 Deluxe was made in April, they dropped the "A" as mentioned the the copied info Willabe posted.

(https://i.imgur.com/P9CMk7v.jpg)

Oh and... The power transformer changed again right before the changeover from brownface to blackface. The later '63 6G3 Deluxe amps have the 125P23B transformer, same as the first Deluxe Reverb amps. Below is the PT of my July 1964 Deluxe Reverb.

(https://i.imgur.com/KXBFSB6.jpg)