ST 35 new owner questions

[Louie3]

Just bought a built ST 35, have a few questions:

How often does one set/check the bias?

My main speakers are nominally 6 ohms, 4 ohm tap?

Can these amps be bridged (strapped)? and if so, is anybody out there using two as monoblocks and how do they sound?

Any reason I should NOT use EAT tube coolers on the power tubes?

Still adjusting the system to suit the slightly lower power, but on first read, this is a very sweet change of pace (normally Classe' DR 8 monoblocks).

I am sure I will have more qx, but that's all for now.

Thanks

[Shannon Parks]

The bias is a slightly adjustable cathode bias circuit. My experience is that you won't need to adjust it after initial adjustment, and only after tube rolling. FWIW, I've considered even changing the parts list to omit the adjustment - make it four fixed values.

[EWBrown]

I just pre-set the resistance to either 400 or 430 ohms, and let it play from there, and check the adjustments after several hour's operation.

I find that the J/J EL84s start out better at 430 ohms, and most other 6BQ5, EL84 and 6P14Ps start off best at 400 ohms.

If you want to save on parts, just use a 390 ohm, 2W resistor, and optionally keep the 1/2 watt 10 ohm resistor in series, to use as a convenient test point for cathode current, and bypass as usual with 220 to 470 uF, 35V cap for each tube.

Since this isn't exactly heart or brain surgery where narrow preccision is a MUST, 5% resistors are more than good enough.

I admit to being overly "anal" with a DVM, and trying to needle the current to exactly 35.00 mA, but that is a Mission Impossible, to keep it that precisely stable for long... Yellow_Light_Colorz_PDT_04

35 mA +/- 3 mA is OK, and any sonic differences would need an array of expensive laboratory equipment to measure.

There is a third option, the Rev D boards can accomodate an LM317 current regulator, and a 36 ohm resistor to set 35 mA, but this is best applied to SE Class A operation.

I "surgically" modified one REv D board to accomodate PP 6S4As, with 325V B+ and 25 mA cathode currents, and it works at a relatively low power level, and I have yet to build it into and onto a chassis.



Either approach is far more preferable to the original shared 95 ohm, 5WW cathode resistor.

/ed B