Traynor YBA-4

[1blueheron]

Last night got the light bulb limiter assembled and it lit very dimly.

Plugged it in directly tonite and took readings.  Here is the result with line voltage of 121V.

V5

Pin 3 = 461
Pin 4 = 456
Pin 5 = 39.8
Pin 8 = 31mV

V4

Pin 3 = 457
Pin 4 = 453
Pin 5 = 39.8
Pin 8 = 31mV

V3

Pin 1 = 217
Pin 2 = 39
Pin 3,8 = 41
Pin 6 = 255
Pin 7 = 38

V2

Pin 1 = 117
Pin 2 = 27
Pin 3 = 28
Pin 6 = 184
Pin 7 = 0

V1

Pin 1 = 209
Pin 2 = 0
Pin 3 = 1
Pin 6 =218
Pin 7 = 0
Pin 8 = 1

[1blueheron]

Plan to check resistors tonight for drift and see how they look.

Would like to go ahead and play with installing the additional screen resistors as suggested.  Is this the correct/best way to add them?

The amp sounds much better with the new 6CA7 tubes. 

There is a slight "rushing of wind" type noise when the amp is turned on.  Not a hum, more like white noise.  Any ideas on the cause?

[Willabe]

Would like to go ahead and play with installing the additional screen resistors as suggested.  Is this the correct/best way to add them?

Yes, that's fine like that. But keep the lead on pin 4 short, it is a grid stop R. Grid stop R's work better/best with a short lead.

[1blueheron]

Would like to go ahead and play with installing the additional screen resistors as suggested.  Is this the correct/best way to add them?

Yes, that's fine like that. But keep the lead on pin 4 short, it is a grid stop R. Grid stop R's work better/best with a short lead.

To keep the R lead shorter, maybe I should solder one end to pin 4 and terminate the other end directly on the tube socket chassis screw beside it.

[Willabe]

To keep the R lead shorter, maybe I should solder one end to pin 4 and terminate the other end directly on the tube socket chassis screw beside it.

What????

Your talking about the screen grid R correct? That has dcv on both ends.

Just solder the R to pin 4 1st. Keep the lead ~1/4". Then run the R over the top of the socket, you run that R going to pin 6 up in the air a little, on an angle, so it's lead will be a little longer.   

Just looked at your drawing again, it's wrong. Pin 6 does not get grounded. Pin 6 gets the feed for the screen grid dcv. 

[1blueheron]

It appears I was confused between screen resistor and a grid stopper. 

I think I now understand. Screen resistors should go between pin 4 and B+2.  I would just be using pin 6 as a junction point for B2 feed.  You are saying to keep the resistor lead between Pin 4 and the body of the resistor as short as possible.   I will move the B+ lead that is presently tied to V5 Pin 4 from the existing 470R 10W,  to  Pin 6 of v5 and then to pin 6 of V4.   Resistors go up and over from pin 4 to pin 6.  Is this all correct? 

[sluckey]

You are saying to keep the resistor lead between Pin 4 and the body of the resistor as short as possible.

That's not right! The resistor leads need to be long enough to allow the resistor body to sit about a half inch above the socket. Some people like to bend the leads over so the resistor is not sitting directly above the socket but that means you need adequate space around the socket. I like to do it this way...

     http://sluckeyamps.com/6v6plexi/P-6V6_05_big.jpg

[Willabe]

That's not right! The resistor leads need to be long enough to allow the resistor body to sit about a half inch above the socket. Some people like to bend the leads over so the resistor is not sitting directly above the socket but that means you need adequate space around the socket.

You want the screen R up in the air above the socket because of heat?

That's why I run the other end up in the air some. Like 22.5 to 30 degrees angle. I would think 3w metal oxide R's should be fine.

Most, if not all Traynor's have their chassis sitting with tubes up, like Marshall's, not tubes down like Fenders. So a lot less heat in the chassis. Even Traynor combo amps. They have a wooden shelf in the cab that the chassis sits on that divides the speakers from the amp section of the cab. 

Just solder the R to pin 4 1st. Keep the lead ~1/4". Then run the R over the top of the socket, you run that R going to pin 6 up in the air a little, on an angle, so it's lead will be a little longer.

[1blueheron]

Thanks for the expert feedback.  Sometimes I need to be spoonfed.

Checked my stash of supplies and don't have much in the 3W metal oxide bin.   Will need to order some before I can complete the updates.

[sluckey]

470Ω/3W metal oxide is not the only option. Marshall used a lot of 1K/5W screen resistors on their 50 watt amps.

[Willabe]

470Ω/3W metal oxide is not the only option. Marshall used a lot of 1K/5W screen resistors on their 50 watt amps.

It's better, gives the screens more protection. (The 1K/5W.)

[1blueheron]

I assume you are refering to the 5W 1k  Xicon wire wound  resistors like Hoffman sells for Marshalls?  I can check and see what I have in wire wounds.

[1blueheron]

Is it necessary to jump up in watt rating when going from Metal oxide to wire wound?  If ordering Metal oxide, is it better to just go with 5W rather than 3W (if space is not a concern) 

[thetragichero]

it's just easier to find 5w wirewound than 3w. either should be sufficient.
P = I²R. 5W = I² * 1kOhm. I² = 5W / 1kOhm. I = sqrt (5W / 1kOhm) = 70.7mA. EL34 max screen current 50mA so by the time your resistor is dying your screens have melted
3W/1kOhm is 54.4mA, might act as a 'fuse' for the screens but if you're relying on resistors as 'fuses' it's rather poor design
3W/470Ohm it's 79.9mA