Ye Olde Screed Resistor Thread

LV, I was thinking about this while I had a '57 5E5A on the bench. If you are building this circuit, then things get simple since imho one does not have to do what FendeR did....and I can't think of any reason to do things the way Fender did back then. We had a little thread about it.
For one thing, I would think you are running a twisted pair for the heater filaments, so there is no reason to run that ground from pin 8 through the blank pin 1 to pin2 and then to ground..(..not that there was any reason for them to do it that way back then, right? They may have done that as a continuation of the process of taking the metal shell of the metal power tubes to ground. This reason was proposed by a tech who has a long experience.) Take the cathode to ground. Use pin 1 for the bias grid stopper contact going to pin 5 and use pin 6 for the connections for the screen grid to pin 4.... Just like the later Fender approach to those sockets.
Side note...I was looking at that original way of wiring that socket because I noticed how high the screen grid voltage was in that circuit.....3 volts above the plates in that '57.....385 on the screen, 382 on the plates. A fellow member...Fred Mertz iirc...suggested that one could set up things to run that screen with 3 different voltages for 3 different types of operation. Interesting way to get just a bit of variety out of what I think is one of the better Fender circuits from the tweed era. If that '57 had been mine or if the owner had wanted to afford it, that would have been done because the amp was not a pristine all-original...and the change is not of an intrusive nature, anyway.

 

Ah, to have some of those smaller hands that Emily or Lily had, right? Those tweed chassi can pose an access problem, no doubt. Good luck with the project....and let us know how it things go.

 

Get yourself an early 1960s 6v6 Revererocket.
When you're done changing out the electrolytics you'll think "dang there's a lot of room in a Fender tweed chassis."
Or just get some hemostates at the local cheap tool store.

As far as the E series tweed wiring my 5E7 is wired like an original. I've been side tracked with other things since I built it so I haven't really messed with it. Sounds good though.

 

I'm adding a screen-stopper to my 5E8A build. My plan is to do a j-bend splice from the wire to the resistor, put heat-shrink tube over the splice and attach the other end to the tube socket.


-tINY

 

Yessir, that is the basics of what I was saying. IF you would be so kind to let us know what that screen grid voltage is and what your plate voltage is when you get it wired up. The last part of my sugggestion was that there could be options as to what voltage is applied to the screen.

 

isn't that how Fender did it? seems to me my Fender amps are just like that.

But I guess it's 6 of one, half-dozen of the other. You can lay the heater wires on the chassis and fly the leads over them; or you can fly the heater wires and lay the leads under them, along the chassis.

 

The twisted pair can be lain low and toward the back of the chassis in order to allow sone access to the circuit board, right? This is how Fender when they went to the twisted pair filament wiring later in the tweed era.
Here is a picture of a build that gives us just a peek at what should be done, imho. 5th picture down shows the best aspect of the filament wiring.

https://sites.google.com/site/stringsandfrets/Home/bassman

 

your example and the one I showed are done exactly the same way.

 

I found that pic just looking for an photo example of how the twisted pair was laid out. I haven't studied anything else they did there.
I prefer the heater filament layout on the pic in that link I gave you to the black and white wiring above. I prefer not to have those heater filaments in the way on top of the sockets in these cramped tweed chassi. That looping around the socket is not the problem I have with the way Fender did their filament wiring on those earlier tweeds. I prefer to see twisted pairs for noise reduction. If you want, you can maintain the original approach by grounding one side of the heater filament--pin 2 on the power tubes--- by itself, then ground the cathode by itself..thereby freeing up pin 1 for the bias grid stopper resistor. That frees up pin 6 for the screen grid resistor...that Fender did not use in these amps, either. But...as I understand it....the twisted pair eliminates some noise.

 

I like to tie pin 1 and 8 together to be EL34 compatible so this is how I installed screen resistors on my 5E3:

 

When I was looking at that '57 5E5A; I decided that if I wanted to do anything there, I woudl want a small terminal strip to support those screen grid resistors. I like to use 5W sandcast wirewounds for the screens, and they have some weight.

Side note: I had an EBS T90 bass head open this afternoon...non-operative condition.
The interior fuse was burn. I looked around and told the owner: "I don't like this." while pointing to a bunch of huge 15W sandcast resistors that were standing tall off of the chassiss...supported only by their solder contacts and a dab of glue holding them in duets. You guessed it.....two of those huge resistors were torn loose...one wire broken at the resistor....two legs loose on another...one of them never had a chance....you could see the bad solder joint on the solder 'blob'. That was a really poor way to install those resistors...but I don't know if there would be much of an alternative. They don't build amps any more. side side note: the recent buyer thought he had bought a 'boutique' amp. ON the back....blacked out with a marks-a-lot..."Made in China".
HE is getting his money back on the buy.