Deluxe 6G3 Voltages a bit low.

[BruceJ]

I built a 6G3 a few years ago. Straight away from the schematic no mods etc. I did however use a donor set of Transformers. I don't remember what they came out of since I moved and misplaced that documentation. I do know it ran at least 1 6V6 as I always made sure I matched trannys to at least that end.  At any rate, the voltages are running about 40 volts or so to low. Is there any easy way to boost it to get these voltages up. The amp sounds "OK" but it just doesn't have the soul it should. I have tried an "SS" recto but that didn't get it.

          pin2   pin4       pin6   pin8
5Y3     340   303AC    340   303ac

            pin3    pin4    pin5
6V6      334      333    -26
6V6      328      327     -26

             pin1   pin2   pin3       pin6   pin7   pin8
12AX7   211    10      15          204   10      15
12AX7   160    0        1.1         187    0       1.6
12AX7   152    0        1.3         144    0       1.3


Bruce

[sluckey]

You will likely need to replace the PT. Easy is not necessarily cheap.

[BruceJ]

That was kind of what I expected. Not necessarily what I wanted to hear. I guess that would leave me with a set of trannys for something else I don't need. I love this addiction.



Bruce

[eleventeen]

Couple things about your post strike me a bit odd. Maybe I am being overly picky. [re: 6G3]

I do know it ran at least 1 6V6 as I always made sure I matched trannys to at least that end.

This 6G3 is a push-pull amp w/dual 6V6....if the "it" you are referring to is the donor amp.....maybe you are saying the PT came from donor #1 and the OT came from donor #2? Two different donors? PT from a light-duty something and just not cutting it? That would make sense.

At any rate, the voltages are running about 40 volts or so to low.
pin2   pin4       pin6   pin85Y3     340   303AC    340   303ac  <-----you should see the B+ (DC) on pins 2 & 8 and the AC on 4 & 6. Typo?

pin3    pin4    pin56V6      334      333    -266V6      328      327     -26  <----this looks as you say 40-50 volts low.

I would just check once again w/a SS rectifier. A 5Y3 usually imposes a solid 50 volt loss. The amp may not have the oomph you want, but it's hard to believe that throwing in a SS rectifier doesn't jack the B+ very noticeably. (Talking about to a meter: It may not seem to get all that much louder, but those higher volts should be there.)

[BruceJ]

Couple things about your post strike me a bit odd. Maybe I am being overly picky. [re: 6G3]

I do know it ran at least 1 6V6 as I always made sure I matched trannys to at least that end.

This 6G3 is a push-pull amp w/dual 6V6....if the "it" you are referring to is the donor amp.....maybe you are saying the PT came from donor #1 and the OT came from donor #2? Two different donors? PT from a light-duty something and just not cutting it? That would make sense.

**** They were a matched set. Wish I had the documentation I had taken but like I said, I moved and lost it.******

At any rate, the voltages are running about 40 volts or so to low.
pin2   pin4       pin6   pin85Y3     340   303AC    340   303ac  <-----you should see the B+ (DC) on pins 2 & 8 and the AC on 4 & 6. Typo?

**** yep, looks like a typo to me. The 5y3 voltages are correct just low******

pin3    pin4    pin56V6      334      333    -266V6      328      327     -26  <----this looks as you say 40-50 volts low.

I would just check once again w/a SS rectifier. A 5Y3 usually imposes a solid 50 volt loss. The amp may not have the oomph you want, but it's hard to believe that throwing in a SS rectifier doesn't jack the B+ very noticeably. (Talking about to a meter: It may not seem to get all that much louder, but those higher volts should be there.)

***** I am going to put the SS rect back in and check again. I may get a GZ34 to put in also. If my memory serves me it should only drop the voltage by 15-20V. I don't really have a problem getting the "correct" transformer set, but why spend the coin if I don't have to. I really like the tremolo on this amp, but the way it is it's just thin and the tone is just lifeless.******

Bruce

[sluckey]

The Fender schematic says the PT puts out 333VAC. You only measure 303VAC from your PT. That accounts for the voltage difference.

[eleventeen]

Try the SS rectifier again, maybe it gets you halfway there and you'll be OK. Just so we're clear, the SS rectifier is a tube-base with diodes in it? Do those have anything inside other than two (or four) 1N4007 diodes in place of the rectifier tube? Because 303-0-303 thru a pair of diodes should produce 303* 1.4 = 424, knock off 25-35 volts for loading, I see no reason why that wouldn't get you 375 volts or so which should be just dandy.

[BruceJ]

The Fender schematic says the PT puts out 333VAC. You only measure 303VAC from your PT. That accounts for the voltage difference.

**** that is correct******

Try the SS rectifier again, maybe it gets you halfway there and you'll be OK. Just so we're clear, the SS rectifier is a tube-base with diodes in it? Do those have anything inside other than two (or four) 1N4007 diodes in place of the rectifier tube? Because 303-0-303 thru a pair of diodes should produce 303* 1.4 = 424, knock off 25-35 volts for loading, I see no reason why that wouldn't get you 375 volts or so which should be just dandy.

****I am going to put it back in. I am using 1N5404 diodes. Probably what I had on hand at the time. They are also mounted to a small board since I have a bit of extra room.****

Bruce

[BruceJ]

The SS rectifier got me to 356 on the 6V6's. Still think it's about 20 low. I will probably spring for the right trannys and a GZ34 so I can get back to the tube rectifier. Should be pretty sweet soon.

[eleventeen]

356 volts compared to the 365 called for on the diagram is a miniscule 2.5% off in a +/- 10% world. The Fender layout dwg claims +/-20%! If your amp isn't doing what you want with voltages 2.5% low, I am very skeptical that replacing the PT will give you what you're looking for. But I am a lot less sensitive to nuances of sag and amp dirt because I play in a cleaner style. It wouldn't be my idea of a good time to blow $75 on a tranny, carve out the chassis metal (assuming a diff cutout size than what you have) with the rest of the amp already built, and not achieve a rousingly improved result. That's my comment, FWIW.

[BruceJ]

When I bent and machined the chassis, I cut it out for the correct PT but retrofit this one in. I may leave it for now and look elsewhere to find the sweet spot in the amp, that I am looking for. When you build amps from scratch including cab,chassis,board,etc... You really want it to be the best it can be. I have built a few that ended up back in the parts drawer, but this one has something special, I just have to find it.

Bruce