Fender Brown Tremolux 6G9-B

[luthiernc]

I picked up this amp for free. Brown faced ’62.
The power transformer is a 125P6A/68409
The speaker transformer is a 125A6A
 
Works fine after replacing all filter caps but the schematic says B+ should be 365V and I read 455V. Above 20% note.
Schematic bias says -36V but I read -46V
Line voltage is 119vac
GZ34 rectifier.
 
Is this B+ a power transformer problem? Or is it 1962 vs 2019 line voltage?
 

[vampwizzard]

First of all. Holy cow thats a hell of a pickup. The voltage still seems a little high.. should be a direct ratio increase from 110 to 120 (8%) and youre running 20% hot. I would check the incoming voltage to pins 4 and 6 on the rectifier. What did you replace the filter caps with? Same values?

[shooter]

If it's a keeper, put a couple 1ohm R's cathode to ground so you can get an easy measurement of PA tube current, do the math to be sure you can bias to ~70ish%. I suspect you can dial it below max, then you can decide which way to go to lower plate B+, if anything...zener, dropping R, new PT etc.

[Ed_Chambley]

And I am looking for a Fender chassis 23" wide and you have one now.  Does yours have EL84 power tubes?

[shooter]

EL84 power tubes

Ed you made me look 
I'm not a fender guy, I thought leo only used 6V6 or 6L6 that far back, I'm enlightened 

[Ed_Chambley]

EL84 power tubes

Ed you made me look 
I'm not a fender guy, I thought leo only used 6V6 or 6L6 that far back, I'm enlightened 

Did you notice the voltage?  So high Leo had to have something to do with it.  I believe Timbo built one a while back.  I owned one in the late 70's, but I also owned a Marshall Super lead and beck then Karaoke was not around so people actually went to listen to the band and had no desire to sing.  It is a lot different without the words on a teleprompter and radio exact music.  How F'n boring.

[vampwizzard]

The EL84s were in the A model i believe. Bona Fide tube cooker lol. (did a lot of research on el84 amp topologies)

[luthiernc]

First of all. Holy cow thats a hell of a pickup. The voltage still seems a little high.. should be a direct ratio increase from 110 to 120 (8%) and youre running 20% hot. I would check the incoming voltage to pins 4 and 6 on the rectifier. What did you replace the filter caps with? Same values?

I replaced all 5 filter caps with 22uf @ 500v (the amp had 16uf @450) and the PT output is 330-0-330vac.

[luthiernc]

And I am looking for a Fender chassis 23" wide and you have one now.  Does yours have EL84 power tubes?

6L6GCs

[pdf64]

I think it’s normal for many Fender models of this era to have actual circuit voltages somewhat higher than their schematic nominal values, with the cause being both the modern higher mains voltage and seemingly different PT specs being used for production units.
The heater voltages from the PT are a key reference point here. When the supplied mains voltage matches the intended primary voltage, then they will match the nominal 5 and 6.3V (loaded).
A variac or mains bucker can then be used to tweak the mains, in order to get the heater supplies within spec (preferably <5% above nominal).

[vampwizzard]

Did you measure those PT values or did you take them from the datasheet? looks correct for 120V vs 110.. if it were me id check the components running over to the trem circuit off that first secondary. If the resistors in the power circuit all check out id start looking at using a different rectifier tube with more DCV dropoff. GZ34 has a theoretical drop of 10V, id look at like a 5u4 (44v drop) or a 5Y3 (60v drop).

FWIW Nashville has gotten on the brown/blonde vintage amp train and they like to use Amp RX BrownBoxes to attenuate the incoming AC. Mostly seen it on deluxes and princetons but id assume the same thing would be beneficial for the tremolux. Dream amp btw. super jealous and would love to see some pics of this beast!

Hope that helps

[luthiernc]

Did you measure those PT values or did you take them from the datasheet? looks correct for 120V vs 110.. if it were me id check the components running over to the trem circuit off that first secondary. If the resistors in the power circuit all check out id start looking at using a different rectifier tube with more DCV dropoff. GZ34 has a theoretical drop of 10V, id look at like a 5u4 (44v drop) or a 5Y3 (60v drop).

FWIW Nashville has gotten on the brown/blonde vintage amp train and they like to use Amp RX BrownBoxes to attenuate the incoming AC. Mostly seen it on deluxes and princetons but id assume the same thing would be beneficial for the tremolux. Dream amp btw. super jealous and would love to see some pics of this beast!


Hope that helps

Great idea about the rectifier tubes! I did measure the output of PT. Here are some pictures of the amp burning in with "no noise or sizzle). I am re-tolexing because some DA sprayed 3 different colors on the blonde tolex and it wouldn't come off. Sorry my file size is too big to upload and I don' know how to reduce the size.

[shooter]

my file size is too big

try sending it to your phone, usually downsizes it.
I just open the file (jpg) with whatever viewer you have and re-size to something in the Kbye range

[luthiernc]

Thanks for the resize help, Shooter.

[vampwizzard]

She will be pretty! Awesome stuff.

[Gone_Fishing]

Older thread but I was looking for a cab for my 6G9-B. I bought the chassis only and all the transformers were toast. I got it from a guitar store because it had set their for over a decade and the owner who burnt it up because of some sort of moding gone wrong that he did, “disappeared” after they told him the bad news and they figured it was because he didn’t want to pay the bench charge, which I did and not much more.
   From all the research that I did after I got mine, I’m pretty sure that all B models that came out as Bs with 6L6s had the Normal channel first and the Bright channel second and the first 6G9 and early As which were converted to 6L6s had the Bright channel first and the Normal channel second when looking at the amp from the front.
   I have never seen that written anywhere but it’s obvious in pictures of each model  and from Fender’s schematics and layouts.
   My amps circuit and board was definitely a B model and the PT had a 48409 only number.
   I wired it to a 6G9 circuit with EL84s and got replacement transformers from Mercury and put the original 48409 bell on the PT.
   Very cool amp but not a whole lot of difference between it and my 66 blackface Tremolux.
   The voltages are too high and they were  back then also, but I don’t play it much and that’s probably the reason why it hasn’t smoked yet. I’ll probably convert it back to its original birth as a B model some day so I won’t have to worry about it going up in smoke.

[glass54]

Hi luthiernc
I worked on one just over a year ago. Changed the bias cap from 25u/50V to 47u/100V as the raw Bias supply was at  -58V!
I'm in Aussie BUT to confirm voltages I recorded:
236VAC input
HT (Node A) Actual: +435V (6L6GC at 38mA per tube) GZ34 Rectifier. Drawing shows +365V as you noted
Node B: +434V
Node C: +364V
Trust this helps
Kind regards
Mirek

[bmccowan]

6G9-B is the last of the brownface - the Blackface Tremolux specs the same PT and the schematic has the B+ at 415, and the bias at -45V. Fender often neglected to update the voltage specs on their schematics. As you go through the amp and fix issues, you may find the B+ dropping a bit. As pdf suggested, it'd be good to check the heater voltages.
I assume you saved this from a dumpster fate - nice.

I just realized how old this original thread is - so now I am wondering how this amp turned out?

[glass54]

+1, How did the amp work out? 
On the above post I failed to add one more voltage.
Bias at grids was -44V for documented node Voltages and currents.
(All voltages were measured with Fluke 179)
Kind regards
Mirek

[bmccowan]

I have sent Luthiernc a PM asking him to please visit the thread and tell us how the amp turned out. I am always disappointed when someone gets some advice and then lets the thread die without communicating how things turned out. Its like a mystery novel when you get near the end and someone has ripped the last few pages out.

[luthiernc]

Well...after altering the bias circuit a bit and installing 1 ohm cathode resistors in 6L6's the puppy is singing an new song. Got a offer I couldn't refuse from a music store owner and sold it but it was great knowing that I was able to restore this head, tolex and all, with a little help from my friends. Mystery solved!

[Ethan]

My amps circuit and board was definitely a B model and the PT had a 48409 only number.  I wired it to a 6G9 circuit with EL84s....   Very cool amp but not a whole lot of difference between it and my 66 blackface Tremolux.  The voltages are too high and they were  back then also, but I don’t play it much and that’s probably the reason why it hasn’t smoked yet.

Mine is an original 6G9 A and I agree with everything you've said here:  It doesn't sound substantially different than other Fenders of the era that use more typical tubes, the voltages are WAY too high (I had to drop the bias way, way down just to keep it from eating tubes) and the only reason I haven't had any problems with it is probably that I seldom use it.  I'm primarily a bass player anyway but even when I do play a gig on guitar (5% of the time at best) I'm much more likely to bring a smaller amp than to drag a piggyback to a NYC club so the Tremolux stays safely at home and that's probably why it's still alive.  It sounds really nice but I expect I'll sell it eventually.

[Gone_Fishing]

Thanks Ethan,
I never get anyone to agree with me except people who are drinking my beer, and then they only agree that it tastes better than no beer at all, lol.
   If I over looked this, I apologize, but you said that your amp was an A model, and if it’s an original A, it should match an A schematic and layout.
If it has 6L6s and a Bright-Normal faceplate, it’s should be a ***Revised 6G9 with 6L6s.
   I’m still trying to figure out what Fender did with these amps.
If you look at the great layouts and schematics on this website, (Thank you Mr. Hoffman) you will find 4, not 3, versions of the 6G9,
1-The original 6G9 with EL84s-Bright-Normal
2-A layout only of a 6G9, ***Revision converting EL84s to 6L6s———Bright-Normal
3-Original 6G9-A with 6L6s——Normal-Bright 
4-Original 6G9-B with 6L6s——Normal-Bright
   The B model is easy to spot because they have no standby switch for some reason.
   I was curious what exact model your amp is, you said A, but could it be a ***Revised 6G9?
   Again I apologize if I’m not understanding your post.