Help on Fender Blonde Tremolux

Hiro Keitora · From: New York, New York

Thank you so much for all of you...

I got it happening at last!!

Firstable, the model is 6G9, I think it's '61.

The parasitic oscillation with high pitch noise was cured when I swapped the brown and blue leads from the output tranny. I thank Curtis for that.

Tremolo's negative feedback resistor is 27K and 1500 ohm. ( unlike 6G9B, which has 56K or 100K and 4700 ohm). After I replaced all the caps( including 2 of extra 0.03 along with common .01 and .02)Finally, the tremolo is working fine. I mean, finally.

Once again, I thank you all for lots of valuable tips. Truly, truly appreciated!!

Jim Sliff · From: Lawndale California, USA

Hiro - there are a lot of possibilities. When you rewired the amp, did you check for wires *between* or *under* the eyelet board sections? I don't have my Tremolux info handy, but many Fenders run wires that can't be seen, and I've encountered many cases where guys have rewired the visible stuff, not realizing there are unseen wires.

I assume you did a one-by-one tube swap-out? That's the first diagnostic, as you don't even have to crack the chassis to do it. Then I'd try pulling each preamp (including trem) tube in order - iff the noise stops, you hhave narrowed it down to a preamp issue, and probably the section. If it still squeals, it's in the power section. At those points, rechecking wiring and lead dress is mandatory - it sounds like a parasitic oscillation, which makes me think the lead dress is fouled somehow (that is, unless you find a bad tube).

I assume you have tested te amp without a guitar, and with trem both on and off?

Hope that helps -

Jim
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Ken Fox · From: Nashville GA USA

Which chassis number is yours? There are three on the Fender Amp Field Guide. You can start by removing the tube for channel one and re-check the amp. Then channel two and after that try the tremolo tube. that will help isolate where the trouble is, if in the preamp section.

Bill Hatcher · From: Atlanta Ga. USA

What Sliff said!

Make sure the output transformer wires are soldered correctly. You install the tformer backwards and the amp will squeal like that.

Also the wire routing on the circuit board is critical on ALL Fender amps. While the amp is on and warmed up you can move the wires around and sometimes find culprits. Just the correct bend in the wire and getting it closer to the metal chassis will affect the noise floor of the amp. BE VERY CAREFUL WHEN DOING THIS!!!!!!

The old blond amps run do not run off the photo coupler for the vibrato. You will have to trouble shoot the circuit to fix that.

Ken Fox · From: Nashville GA USA

There are 3 different schematics for the amp. The later one (6G9B) did use negative feedback from the output transformer to the inverter stage. The earlier two did not and it will not matter which way the primary leads are connected to the tubes or the secondaries are connected for the speaker output, just a difference in the output signal phase will occur..

As Bill mentioned above, it will matter if you have the later model! It will holler like pig with his tail cut off if those leads are not right. It will put a positive feedback to the inverter stage and put the amp into feedback with itself.

Randy Phelps · From: California, USA

Hiro,

If what Jim told you doesn't fix it...

Check the input wiring. I think you've got a loose ground or an improper ground.

This can be a cause of the oscillation...

I had this problem on an 5F2A I was building.

Jim Sliff · From: Lawndale California, USA

Hiro - if none of the simple troubleshooting methods work it would be real helpful to know *which* circuit you used as a guideline; as Ken mentioned there are drastic differences and while you talk about a blonde Tremolux, if you rebuilt it using a late-blackface circuit we could steer you the wrong way.

Tube swapping and checking jacks is fine, of course. And since you installed a transformer I assume you know how to discharge filter caps and work safely inside the chassis - right>
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Hiro Keitora · From: New York, New York

Thanks everyone! Well, I don't even know exactly what model this is...6G something, but looking at some original pots, I think it's 61-62 ish.

This output tranny I got from Mojo, has 4 ohm lead along with 8 ohm and ground. Currently, the 4 ohm is taped up and not been used. Do you think I should swap ground wire and 8 ohm lead?

In the past, I had funny situation with one amp. With stock speaker in the cabinet, amp sounded great. But as soon as you run that to an extention cabinet, that speaker squeel like pig like you said.

That out put tranny was simply 8 ohm lead only, and as soon as i swap the leads, the problem went away.

But in this Tremolux, when the tube is warm, it sounds quiet, when the tubes start to get hot, then it starts to give that mosquito like high pitch noise. A classic situation of parasitic oscillation to me.

Also the way tremolo kicks in is not right. It's like it works but it won't kick in, or quit like it suppose to do.

I need proffesional help at this point...

<H>

Donny Hinson · From: Glen Burnie, Md. U.S.A.

As I recall, that amp (like most Fenders), has a negative feedback loop - a resistor that feeds some of the secondary speaker voltage back thru the phase inverter. If the feedback resistor isn't hooked up, or is hooked up wrong, you'll get screaming treble and a lot of noise, sometimes with oscillation.

If that's not the case, then one of the bypass caps may be bad, and that's allowing some (unintended) interstage coupling, which can lead to crappy tone and feedback, too.

Jim Sliff · From: Lawndale California, USA

OK, let's get specific:

The ext spkr jack should have a wire off of it leading to a 56k resistor; that's the negative feedback loop. If it's not hooked up, or the resistor is a different value, install the correct one (correct being 56k - 100k; the layout and schematic printed in most books and on the Fender Amp Field Guide are different, and you might have to experiment with the value). Also, the other end of that resistor has one of those "mystery" wires between the boards - it leads to a 4700 ohm resistor that leads to ground. If THAT wire is not connected or that resistor is wrong (or not grunded), you still have a fouled negative feedback circuit.

Since your trem is not working I'd concentrate on the negative fedback loop and *everything* connneected to V3, which is your trem oscillator. Sometimes if the neg feedback loop is out of whack it can nuke the trem in the Fenders using all-tube trem.

The next item to check is the voltage at pin 6 of V3 - should be around 360V, and it comes off the transformer. If you didn't get that wire hooked up that will almost surely solve it.

If that one is there, as I said earlier double-check everything hooked up to V3 - also, play the amp with V3 removed. It won't hurt anything, and might pinpoint things to that tube's wiring.

You have changed that tube, right? That would be the *first* thing to do.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Curtis Boatright · From: friscoTexas, USA

Hiro,i sent you an e-mail. try that first.if no luck feel free to e-mail me.
curtis boatright

Hiro Keitora · From: New York, New York

Oh, man, thank you so much for the tip.
Well, it seems "hooked up" ok, and the tremolo works sometimes; but it still takes a while to kick in.

Removing V3 helped a lot, but still some high pitch noise there when the tubes start to get hot.

Yes, I read a little more than 36oV, so it should be ok I think.

Let me try more...

Hiro Keitora · From: New York, New York

Thanks again folks!!

<H>

Jim Sliff · From: Lawndale California, USA

Hiro- one thing you have not described is what tubes are currently in the amp. Could you post a note listing them? It might provide some other clues.

And so we're not duplicating efforts, what did Curtis suggest?
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Hiro Keitora · From: New York, New York

It now has 6L6s and it works good. I have a schematic for EL84s too, but I need to clean this up one at the time.

Curtis suggested to swap the lead wires to the output tubes from output tranny. The leads has color coded, and I wired accordingly, but I guess it was out of phase.

<H>

Ken Fox · From: Nashville GA USA

Was that a Hoffman output transformer? I have had several that were out of phase. There color coding is just plain backwards, or at least it was on the transformers I used for 135 watt Twins and Bassman amps.

Michael Brebes · From: Northridge CA

Hiro, in the future can you please post a new reply INSTEAD of completely writing over your original post. Because you did that, I (and any others that didn't see the original post) don't have a clue what your original problem was since you edited it out. As far as I am concerned, this post will help no one who might have a similar problem in the future.
_________________
Michael Brebes
Instrument/amp/ pickup repair
MSA D10 Classic/Rickenbacher B6/
Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso

Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100

Jim Sliff · From: Lawndale California, USA

Hiro Keitora · From: New York, New York

Sorry, guys. I didn't mean to confuse anyone. Michael, you are absolutely right, I was only thinking about this "thread" but as an archival information, I should have left the original questions and everything. I'll keep that in mind in the fututre.

Jim, yes, EL84( mini 9 pins) are diffrent from 6L6, but I figured if I wanted to, I could use "THD yellow Jacket" to convert 8 pin sockets of 6L6 to EL 84 for fun. That's why I left it with regular 8 pins.
It offers more flexible options I thought.
But, in reality, in the head cabinet, I'm not sure tall EL84 with Yellow jacket sockets even fit in the cabinet unless I remove chasis to re-tube them. But that's another story.

<H>

Hiro Keitora · From: New York, New York

Ken, This was Output tranny was sold by Mojo, but I don't know who Mojo buys these from.

Years ago, I bought an output tranny from Rodgers, and his tranny was out of phase. But i don't think he made the tranny, he was just a distributor.

<H>

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