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[TurbOSquiD77]

Is it possible that I could run with the 237 Ohm resistors at R1 on the low current board? Trying voltage test....

6080, 12BH7A, 6005's, 237 Ohm resistor at R1 on Low Current board:
Terminal Voltage (DC)
Low Current C4S
IA 150V   150V
      OA 60-90V  47.6V
KregA 3-6V   5.73V
bRegA 150V   150V
IB 150V  148.9V
      OB 60-90V   48.8V
KregB 3-6V  5.86V
bRegB 150V  148.9V

High Current C4S
IA 190V 192V
OA 150V  150V
bA 0V  .3mV
IB 0V   .6mV
      OB 90-110V  77.1V
bB 150V   150V




Tung-Sol 5998, GE 12BH7A, GE 6005's, 470 Ohm resistor at R1 on Low Current board:
Terminal Voltage (DC)
Low Current C4S
IA 150V   150V
      OA 60-90V  35.1V Damn near the same with 6080
KregA 3-6V   5.42V
bRegA 150V   150V
IB 150V  148.9V
      OB 60-90V   36.3V  Damn near the same with 6080
KregB 3-6V  5.45V
bRegB 150V  148.9V

High Current C4S
IA 190V 193.2V
OA 150V  148.9V
bA 0V  .1mV
IB 0V   0-3mV
      OB 90-110V  51.4V (5998)  68.5V (6080)
bB 150V   148.9V


I'll give her a listen with the 237 Ohm resistors at R1 Low Current board - 12BH7/5998.

Happy weekend!

[TurbOSquiD77]

.... and while doing further research I've found that:

"Yeah, ~105V is on the high side, 55V is very low, 88V is in the safe zone.

Those 470 Ohm resistors you linked to will work well with the E80CC.  For the 12BH7, try a 200 Ohm resistor to bring the plate voltage up.

-PB"

I was thinking that running the 237 Ohm resistor with the 12BH7 and 5998 was okay, and the voltage drop was normal - something to do with the 5998 maybe. I was wrong and should not be running the amplifier out of the allowed range of measurements.

I listened with 237 Ohm resistors at R1 - 12BH7(A)/5998 and I didn't like it as much as the Philips ECC82. I'm going to throw the ECC82 back in until I grab some 200 Ohm resistors - then I will try the 12BH7 again. I'd rather not run low voltage for an extended period of time. From what PB was explaining, it's not good especially with the 5998's higher transconductance and lower plate voltage.

Definitely trying to find a good single E80CC! Sounds awesome from what I read. 

-T

[TurbOSquiD77]

For the books: 5998/ECC82/6005's - using 237 Ohm resistors at R1 on the Low Current C4S board.



Terminal Voltage (DC)
Low Current C4S
IA 150V   150V
       OA 60-90V  76.2V
KregA 3-6V   5.70V
bRegA 150V   150V
IB 150V  148.9V
       OB 60-90V   76.5V
KregB 3-6V  5.92V
bRegB 150V  148.9V

High Current C4S ( / indicates left and right High Current board measurements)
IA 190V 192.6/192.3V
OA 150V  148.9V/150V
bA 0V  .3mV/.5mV
IB 0V   .2mV/.5mV
       OB 90-110V  84.9V/84.3V
bB 150V   148.9V/150V

[Paul Birkeland]

I'm sorry, I'm mixing up the resistor mod for the E80CC with what you need to do for the 12BH7.

Try an R1 of 124 Ohms on the low current C4S R1.  Post your measurements for Kreg on each side after you've done this.  R1A on the high current C4S boards may also need an adjustment in value as well.

-PB

[TurbOSquiD77]

I'm sorry, I'm mixing up the resistor mod for the E80CC with what you need to do for the 12BH7.

Try an R1 of 124 Ohms on the low current C4S R1.  Post your measurements for Kreg on each side after you've done this.  R1A on the high current C4S boards may also need an adjustment in value as well.

-PB

Will do! Would you happen to know what value resistor I'd be looking at to adjust R1A on the high current boards? Ballpark range if exact value is unknown - I'm looking to order some resistors of different values to have on hand. 

6SN7/(GT) looks interesting as well. I read the 12BH7 is most of the 6SN7 minus a bit of tubey sound.

[Paul Birkeland]

If you want to buy some resistors, values between 11 and 12 ohms are likely what that R1 should change to. Also changing the 270 Ohm 5W resistors out to 300R 5W resistors will alleviate some C4S thermal load.

[TurbOSquiD77]

Also changing the 270 Ohm 5W resistors out to 300R 5W resistors will alleviate some C4S thermal load.

Awesome. Looking at Mouser for 300R 5W:

Vishay/Dale RE60G3000C02 chassis mount wirewound 1%
Ohmite 805F300E chassis mount wirewound 1%
Vishay/Draloric AC05000003000JAC00 Cement Filled Ceramic 5%
Ohmite TUM5J300E Cement Filled Ceramic 5%
Xicon 280-CR5-300-RC Cement Filled Ceramic 5%

I read inductive types are good, and chassis mount types need proper chassis surface area for the heat sink to function at optimal temps. Unsure if 1% tolerance is favored.

[TurbOSquiD77]

Interesting....

The amp has been on for 5 hours. No headphones, and no RCA's connected (listening to other amp).
I go upstairs for an hour and come down to the power transformer dissipating heat into the air more than usual.
The chassis is hotter than usual. Slight smell (if any).
Rapidly fluctuating pissed off cyborg noise from the power transformer. It's done this before, and during my voltage tests, but not as audible.

Took quite a while for the PT-8 to cool down.
Fuse looks good.

Sleep.

 

[Paul Birkeland]

An angry power transformer will come with voltages that aren't what they are supposed to be.

[TurbOSquiD77]

Agreed, haha.
Forgot to solder an LED and resistor after cleaning up some solder joints. Fixed, voltage test, all is good. E80CC showed up today so I thought I'd give her a shot, and then the 12BH7A.


5998/E80CC/6005's:
470 ohm at r1 on low current board - with e80cc

Terminal Voltage (DC)
Low Current C4S
IA 150V    150.1V
OA 60-90V  67.3V
KregA 3-6V   5.45V
bRegA 150V   149V
IB 150V  149.1V
OB 60-90V   64.1V
KregB 3-6V  5.37V
bRegB 150V  150.1V

High Current C4S ( / indicates left and right High Current board measurements)
IA 190V 193/192.9V
OA 150V  149/150V
bA 0V .3/.5mV
IB 0V  .3/.5mV
        OB 90-110V  74.4/76.8V
bB 150V   149/150V




5998/12BH7A/6005's:
124 ohm at r1 on low current board

Terminal Voltage (DC)
Low Current C4S
IA 150V   150V
OA 60-90V  63.3V
          KregA 3-6V   6.40V
bRegA 150V   148.9V
IB 150V  148.9V
OB 60-90V   65V
          KregB 3-6V  6.59V
bRegB 150V  150V

High Current C4S ( / indicates left and right High Current board measurements)
IA 190V 195/194.7V
OA 150V  148.9/150V
bA 0V  .3/.5mV
IB 0V   .3/.5mV
           OB 90-110V  75.3/73.2V
bB 150V   148.9/150V


I have a few 1/4 W resistors between 11 and 12.1 Ohms. Also picked up a few different brands of 5W 300R wirewound ceramic/cement resistors. 


Thank you Paul I appreciate you giving your knowledge. Hit me with explanations if you could. I'll make sense of them, and I like figuring things out.


-T

[Paul Birkeland]

Yeah, you could go down to 12.1 for R1A on the high current C4S for each side.  This will give the 6AQ5's more current, as we want the cathode follower and shunt regulator to run roughly the same current.

When you pull more current through the circuit, you pull more current through the power supply resistors.  That is the reason for my recommendation to go to a 10W part.  When you set the C4S to deliver more current, the MJE5731A will have to dissipate more heat.  By going to a 300 Ohm resistor in each leg of the power supply, that effect is mitigated by lowering the voltage available at the input of the C4S.

[TurbOSquiD77]

Awesome, I will try and see how she performs!

Just to clarify.... should those be 5 or 10 watt 300R resistors in the power supply? I have a few types of 5W ceramic/cement.

Is Kreg okay, or will the other changes adjust the voltage here?

[Paul Birkeland]

5W parts will be OK for the 300 Ohm power supply resistors.

The Kreg voltage will change when you put the 12.1 Ohm resistors in.  This change will not need to be undone if you go back to the 12AU7 or E80CC.

[TurbOSquiD77]

Nice, good to know! Thank you

-T

[TurbOSquiD77]

5W parts will be OK for the 300 Ohm power supply resistors.

The Kreg voltage will change when you put the 12.1 Ohm resistors in.  This change will not need to be undone if you go back to the 12AU7 or E80CC.

Hey, hope the show was awesome!

I finally got to switch out the power supply resistors to 300R 5W, 124 Ohms at R1 low current, and 12.1 Ohms at R1A on the high current boards. Those wirewounds were quite the task!

Here are my numbers:

5998/12bh7a - 124 ohm at r1 on low current board - 12.1 ohm at R1 on high current - 300R psu resistors
Terminal Voltage (DC)
Low Current C4S
IA 150V   149.2V
OA 60-90V  63V
KregA 3-6V   5.25V
bRegA 150V   149.2V
IB 150V  148.7V
OB 60-90V   64.8V
KregB 3-6V  5.58V
bRegB 150V  148.7V

High Current C4S ( / indicates left and right High Current board measurements)
IA 190V 189.9/190V
OA 150V  148.7/149.2V
bA 0V  .4/.5mV
IB 0V   .3/.5mV
                OB 90-110V  75.2/72.8V
bB 150V   148.7/149.2V



What causes OB to read low?

-T