Bias supply from bridge rectifier circuit

[dynaman1]

I recently picked up the transformers from a Marshall TSL-100 and would like to use these in a 100W project. The PT has a winding that's about 45VCT. The original 100W DSL schem is rather confusing so I'll cite the TSL-60 for reference.

Schem can be viewed here: http://schematicheaven.com/marshallamps/jcm2000_tsl60_60w.pdf

Are the values of C61 and C62 critical? I have some non-polarized 10uf caps laying around...

What does the zener diode "ZD3" do? I don't have any and was wondering what some suitable substitutes might be.

[PRR]

> Are the values of C61 and C62 critical?

If 10uFd wudda worked right, Marshall wudda done it to save the half-cent.

> What does the zener diode "ZD3" do?

Makes the amp melt faster at high line voltage. Someone wasn't thinking.

Are you doing all the +/-15V opamp crap? If not, use the whole W22-W24 45V winding with a single diode, same as we do with a 50V tap. Verify a good resulting bias voltage before you stick bottles in!

[dynaman1]

Thanks for the reply!

Oh heck no, I'm just making a single channel amp. No way would I even think of tackling such a complex circuit. I was simply going to copy Marshall's bias scheme because....I have the transformer and most of the parts.

Indeed, I should know that any value/rating of a given part is the absolute minimum Marshall could get away with.

Ok, so you're suggesting to ignore the center tap, ground one end and treat that winding like the 90V that's found on common Marshall 100W power transformers (ala SLP)?

Perhaps it would be safer for me to simply draw my bias supply from the HT winding, similar to a JCM900? At least I'll know I'll have enough voltage available.

[FYL]

I'd use the 45V winding with a bridge recto and use a low source R failsafe balanced bias system (Sounds like a marketoid blurb, should add many ™ and ® in order to LookVerySerious™®).

Bridge recto: less noise, better stability. Can be used Delon-style if you need up to -100V or so

Low source R: better drive (even if currents are very low), allows for lower grid leak R's, better treble response, less noise

Failsafe: max bias applied if the pot fails

Balanced: set bias level, then bias balance. Allows to use mismatched tubes (or to mismatch currents for a slightly dirtier sound), minimizes noise

Cf. the enclosed schemo - OK, text is in French but verything is self-explanatory.