Resistor's operating voltages?/new question re: rd_psu 8.2k

[ZacharyP]

Hello,

I'm looking to replace all of the resistors in the signal path, excluding RL (will only end up removed when I install the c4s)and the carb comps, with Caddock MK-132 precision power films for the 1.27k and 249k values. 

They are specc'd for 400v max, will there be any issues?

P.S. Is there a loss in performance, specs or sound wise, if I we're to use all Mills non-inductive wirewound MRA-5 resistors in the power supply?

Thanks for reading!

[Paul Joppa]

None of these are a technical problem, though cramming those big resistors into the circuit may prove difficult.

[ZacharyP]

None of these are a technical problem, though cramming those big resistors into the circuit may prove difficult.

The MK-132 is only 0.290" w x h

The tf020 ultra precision are .75"w x .375" h.  I did measurements on the chassis and found they're not so dangerously, or more challenging with concern to mounting components closer than I would in stock form.  Just requires some creative mounting.

The mills mr5 are surprisingly small.

[ZacharyP]

New question, what purpose does Rd_PSU 8.2k resistor serve in the PSU?  I'm always trying to learn new things .

[Paul Joppa]

Together with Cd_psu (22uF/450v), it reduces the hum on the power supply for the driver stage. Because the driver consumes much less current, it can have a much larger resistor than the power stage (680 ohms) and the capacitor can be smaller (100uF for the power stage). The power stage has a relatively high gain (mu is 15.4, compared to 3.8 for a 300B), which means the driver stage needs much lower ripple on the power supply.

A current source (C4S) for the driver would achieve the same goal, but adds significant cost; for that reason it's an optional upgrade. We tried to keep the hum low on even the most basic SEX amp, since it is used by some for headphones.

[ZacharyP]

Together with Cd_psu (22uF/450v), it reduces the hum on the power supply for the driver stage. Because the driver consumes much less current, it can have a much larger resistor than the power stage (680 ohms) and the capacitor can be smaller (100uF for the power stage). The power stage has a relatively high gain (mu is 15.4, compared to 3.8 for a 300B), which means the driver stage needs much lower ripple on the power supply.

A current source (C4S) for the driver would achieve the same goal, but adds significant cost; for that reason it's an optional upgrade. We tried to keep the hum low on even the most basic SEX amp, since it is used by some for headphones.

Very interesting. 

Thins brings up another thought, is the CRCRC filter the 220uf, 680r, 100uf, 680r, 22uf?

  I remember Grainger said in the sex 2.0 the 47uf ps cap was for one half of the 6dn7 and the 22uf for the other half.

Is the 2.1 crcrc PSU the same, and would changing it to a CLCLC effect ideal capacitance and/or effect the role the psu caps have on the tube, if that makes any sense.

sorry for all the questions I recently was diagnosed with neuropraxia so I'll be out of commission from soldering for about 6-8 weeks, I figured this would be a good time to do some learning up on tube electronic theory.

[Paul Joppa]

Best bet is to learn to use PSUD II, the power supply unit designer software from Duncan Amps. It's widely used and usually quite accurate, but there is a learning curve. The hard part is understanding the transformer relations between rated voltage, open-circuit voltage, and equivalent DC resistance.

When you get into power supply chokes, you open the possibility of resonances. A search in the tubediy forum at the audio asylum will turn up far too many posts, most of which are baloney - but not all!

Don't just read the posts - do a lot of modelling yourself with the software. You will learn a lot, and it will serve you well.

[ZacharyP]

Best bet is to learn to use PSUD II, the power supply unit designer software from Duncan Amps. It's widely used and usually quite accurate, but there is a learning curve. The hard part is understanding the transformer relations between rated voltage, open-circuit voltage, and equivalent DC resistance.

When you get into power supply chokes, you open the possibility of resonances. A search in the tubediy forum at the audio asylum will turn up far too many posts, most of which are baloney - but not all!

Don't just read the posts - do a lot of modelling yourself with the software. You will learn a lot, and it will serve you well.

Thanks PJ!  I will do that!

If I remember reading in Morgan Jones text on building (not designing) amplifiers he said with the issue of coupling between mains xformers and OPTs is best dealt with by rotating the transformer (or choke) core 90*, with aligned center. 

I'll search diyaudio more, but I'll assume orienting them like a mains and the 2 OPT, and test and measure results (if I can).

[Doc B.]

The issue of coupling between power transformers, chokes and output transformers is best dealt with by starting with a theory like that postulated in Jones' book and then actually measuring the hum level from the output transformer while you change the relationship of it with the power iron.

[ZacharyP]

The issue of coupling between power transformers, chokes and output transformers is best dealt with by starting with a theory like that postulated in Jones' book and then actually measuring the hum level from the output transformer while you change the relationship of it with the power iron.

That was almost word for word what Jones recommends for lowest level possible.  At the very least a fun expwrimeby.

I'd post my findings now, but with Neuropraxia (haven't seen neurologist yet, doc's best guess) I have difficulty with all aspects of assembly and soldering.  A numb wrist and hand will do that.  Hopefully I can find someone skilled abd local to help, secretly making him a Bottlehead!