Using 330 vdc output in an 18 watt build?

[geoff 1965]

struggling to find an axial lead 20W,there's plenty of stud mount but remember this has to be reverse biased.
you might have to use a 1W zener with a NPN power transistor like the one on the zener2 pdf file.
has the transformer got any numbers stamped on?

[JMPGuitars]

I mentioned the whole reading this site thing, but I think I should link you a couple answers.

Here's a warning regarding the CT method:
viewtopic.php?f=4&t=25111&p=240614&hilit=zener#p240614

viewtopic.php?f=4&t=25065&p=240352&hilit=zener#p240341

search.php?st=0&sk=t&sd=d&sr=posts&keyw ... 4&start=15

[geoff 1965]

wise words as usual from Curtiss! yeah that would be my main concern using either zener or resistor is if they fail!
my other concern is we still have'nt established the full spec of that PT,with those voltages it could easily be from a fender champ type which has 70ma HT supply and 2 amp heater supply which is no good for a 18W.

[kneedeepinit]

so I have narrowed it down to two options which have a history of working and not affecting the sonics of the amp.


the first option is a series of zeners on the CT. The advantage of this design is that it is simple. I can economically change out the zeners once the units is in fabrication in order to end up with the desired B+


https://ibb.co/dnmo7q

the second is to use a low power zener with a variable resistor. The advantage is that I can vary the output voltage until I get exactly what I want.


https://ibb.co/ghp5LA

does anyone have feedback on these options?

[geoff 1965]

have you calculated what's needed like Josh said? very important! this area is going to be subjected to a lot of heat. i.e. the zener2 pdf uses a low value zener because the transistor is the heatsink.if you use a string like the first method but then remove any to get the voltage you're going to reduce the overall wattage and there is no heatsink.
the second method looks okay and the variable resistor would act as a heatsink but they are expensive!
just put my mind at rest with the PT! you've said it's robust and from an organ so i presume it had a push/pull power section not single ended?

[kneedeepinit]

have you calculated what's needed like Josh said? very important! this area is going to be subjected to a lot of heat. i.e. the zener2 pdf uses a low value zener because the transistor is the heatsink.if you use a string like the first method but then remove any to get the voltage you're going to reduce the overall wattage and there is no heatsink.
the second method looks okay and the variable resistor would act as a heatsink but they are expensive!
just put my mind at rest with the PT! you've said it's robust and from an organ so i presume it had a push/pull power section not single ended?

Geoff, the PT came from a Conn organ that had a large number of tubes. I do not recall the model. Other than the voltages, what parameters would you like me to measure?

[geoff 1965]

if it had a large number of valves then it should be okay,i was thinking of the 6.3volt heater supply mainly.1 el84 & 1 12ax7 combined will draw just over 1 amp so ideally you want a minimum 3 amp supply.

[kneedeepinit]

if it had a large number of valves then it should be okay,i was thinking of the 6.3volt heater supply mainly.1 el84 & 1 12ax7 combined will draw just over 1 amp so ideally you want a minimum 3 amp supply.

ok thanks

this PT is a monster, very heavy, almost too large for ease of mounting.

because I have a number of amps already and this is just a recreational build, I am okay with buying some parts and then swapping them to get the proper voltage. I think I am going to go the route of the smaller zener with a transistor as this should get me close on the first try.

Geoff, you raised a possible issue with the cost of the variable resistor. From what I have seen in my limited research, it was not a 50 watt heavy duty type, just a regular trim pot which are quite cheap. Am I making a mistake on that assumption?

[geoff 1965]

not sure! but i would think in a heatsink situation it would have to be wirewound.
i'm suprised nobody who has actually done this B+ reduction has contributed to the post yet!
yeah i think the zener2 method with the transistor looks the best so far,it's from aiken amps and is tried & tested.
having the heatsink looks the safest way,if my sag resistor fails i'll only have an extra 10 volts going into the el84's,if you're zener fails you'll have to book a seat on the next space shuttle to retrieve them!!

[crgfrench]

Sorry, Josh isn't posting that. It would probably be a long while before I even consider that.

Hi Josh -- not to ask for any proprietary trade secrets here, but viz. your EL34 Superlite, I am curious if you have a demo of it we could see/hear (youtube?)

and just generally is your design for it all tube or do you also include SS like a MOSFET?

Best,

Craig

[JMPGuitars]

Sorry, Josh isn't posting that. It would probably be a long while before I even consider that.

Hi Josh -- not to ask for any proprietary trade secrets here, but viz. your EL34 Superlite, I am curious if you have a demo of it we could see/hear (youtube?)

and just generally is your design for it all tube or do you also include SS like a MOSFET?

Best,

Craig

Hey Craig,

My EL34 Superlite is all tube including a 5AR4 tube rectifier. Obviously a SS rectifier could be used in its place.

I will be recording a demo soon since I'm probably going to sell the prototype (which is done, has reverb, and sounds awesome).

Aaaand I'm probably going to post the non-reverb version of the schematic/layout pretty soon. Don't tell Geoff.

Also don't tell him that I'm making a crazier non-superlite version of this (e.g. extra gain stage/different preamp tube). I already drew the schematic and will be finishing the layout soon.

Thanks,
Josh

[crgfrench]

Cool I'm looking forward to hearing that!

For my next build after this briefcase I'm considering doing a slight variation of the Universal Classic 40 LTP EL34 circuit, I think it might be a logical progression from the EL84 Fullerwell for me.