Transformer Questions

[rhinson]

the schematics i know about under the "schematics and layouts" thread in the files section (for the rocket and liverpool) don't list the hv sec ac voltage ratings. these were drawn by mark abbott who has seen and taken actual dc voltages in trainwreck amps and listed these on the schematics---if you have that you don't need the hvsec directly--you can figure it based on the b+ at idle. most any of the "gurus" here will tell you what i've stated---ken ran el84's in the rockets around the 300 -310v on the plates and the pool at about 10-20v higher due to ss rect instead of a 5ar4. moose's 260-0-260 hv sec taps will put you right where you want to be in building these----his power tranny or the pacific (two rock ruby) power tranny (250-0-250 hv sec) are what the builder "gurus" here use when building clones for customers. i posted spec sheets/part numbers for the pacific trannies about 2 yrs ago. rh

From the files section "schematics and layouts":

http://ampgarage.com/forum/files/liverpoolschem.pdf

and another from a "redrawn liverpool" thread

http://www.undustrialdesign.com/guitara ... erpool.jpg

Both show 234VAC.

Like I say above this is confusing - and that's all I'm sayin!

sure i understand the confusing bit there on those-----but they're just not correct. you won't get a 331v b+ from a 234vac pri. i'm betting the guy meant 254 and just had a typo or misreading of a number on a schematic. a 254vac would be a correct one to use here for this trannie. rh

[nickt]

I guess the question would be - why do we have schematics in the files section - some are editted/enhanced versions by forum gurus - that show 234VAC as the OT output voltage?

Because anyone can post to the files section.

In my limited universe, it doesn't seem possible to get a B+1 of 331VDC from a PT secondary of 234VAC tap-to-tap. Looks like an error.

I'm not an expert in any way, shape, or form, on any Expresses. but provided comments myself on some of these. Do like I did; post in the comments thread(s) or send a PM to the author(s).

These schematics both went through a "hey can you see any errors?" stage and I guess no one noticed if they were incorrect. I'm not having a go at the schematic posters - it's great that they posted what they did - thanks!!!

Mostly folks don't worry about how (or if) 234 becomes 331 cause they just order toneslut iron and worry about lead colours. International folks however have to worry because toneslut doesn't do 220/240V.

Now 331/sqrt(2) == 234 which suggests there was verification done. I can't recall what the "correct" maths would be (if the maths is indeed wrong) but the usual divide by root two does give 331.

I suspect a lot of folks might have been drilled in V=IR and all it's permutations for AC/DC capacitance and reactance etc etc back in the day and all that's left is times or divide by root two (0.7 or 1.4). Certainly my residual 30 year old maths for electronics would have led me to concluding 234V was correct - hence the bogus question: why is everyone using 260V?

Apologies to anyone who feels offended by my comments - it was not my intention to upset anyone.

[Fredaxis]

.... International folks however have to worry because toneslut doesn't do 220/240V...

Nick,
I have a 240V Toneslut for my Express
So they exist, even if it may be a small batch.

[rhinson]

yes 234v x 1.4 = 327v (close enough to 331v), but that's a no load figure---and there is considerable load at idle------you get a good 40 -60v drop from that which puts you a good bit below 300v----a bit more even if you used a 5ar4 (for a rocket). so that's what you have to always consider when choosing a particular power trannie for a particular circuit. you could REALLY overbuild the hvsec winding with bigger wire for more current capacity and have less of a drop, or use a less beefier trannie than moose's and have more of a pulldown at idle, and so on. pretty much any tube amp you decide to build with the "normal" stuff we have access to for our diy builds you can expect at least a 20v-30v voltage drop from the no load figure that you calculate (using a ss rect---obviously more to much more if you use a tube rect. depending on which one you use). rh

[Allynmey]

Using Mooses tranny (260V) or my Tranny (268V) I get between 295V and 310V on the plates. I also run them hot.

[nickt]

.... International folks however have to worry because toneslut doesn't do 220/240V...

Nick,
I have a 240V Toneslut for my Express
So they exist, even if it may be a small batch.

Yes I heard about those Apparently international is too much trouble (inventory sits around gathering dust and tying up money) so Moose isn't doing any more (and fair enough too BTW ).

Paulster advised me to call Heyboer direct for a 240V PT - which I did and hey! they started winding before I'd even sent the cash - real old school guys!

[nickt]

yes 234v x 1.4 = 327v (close enough to 331v), but that's a no load figure---and there is considerable load at idle------you get a good 40 -60v drop from that which puts you a good bit below 300v----a bit more even if you used a 5ar4 (for a rocket). so that's what you have to always consider when choosing a particular power trannie for a particular circuit.

I wonder what the *measured" voltage would be under load on the PT? It could be that the measured AC is actually 234V or there abouts - this would line up with folks running a meter over a real wreck. You'd probably only see 260V after pulling all tubes.

Anyway that could explain what the 234V figure really is and where it came from. What do you think?

[rhinson]

yes 234v x 1.4 = 327v (close enough to 331v), but that's a no load figure---and there is considerable load at idle------you get a good 40 -60v drop from that which puts you a good bit below 300v----a bit more even if you used a 5ar4 (for a rocket). so that's what you have to always consider when choosing a particular power trannie for a particular circuit.

I wonder what the *measured" voltage would be under load on the PT? It could be that the measured AC is actually 234V or there abouts - this would line up with folks running a meter over a real wreck. You'd probably only see 260V after pulling all tubes.

Anyway that could explain what the 234V figure really is and where it came from. What do you think?

no i think the 234vac is just a misprint and he meant 254vac. the measured hv sec ac will drop a bit from n.l. to load as you turn from standby to "on", but not much (in really well made trannies not much at all)----usually only a few volts, maybe 5v or less. you can check this yourself with your own builds or with any non-diy tube amps you own/use and rock out on the real drop comes on the b+ from n.l. to load. if you have a hot set of tubes as allyn stated you can have bigtime drop (50 or 60v) even with a ss rectifier. if, for whatever reason, you wanted to use a 5u4 or 5r4 (not 5ar4) or few others you might have a drop of well over 100v from standby to "on". rh

[doctord02]

Paulster advised me to call Heyboer direct for a 240V PT - which I did and hey! they started winding before I'd even sent the cash - real old school guys!

The guys at Heyboer are great to deal with. They have even shipped to me before receiving payment. Thats a class act all the way.

[Dr-Joned]

Thanks for all the input. That did clarify a bit on the voltage. It's nice to get so much audience participation !