Yes, the requirement to use your existing PT is filled very well by this elegant circuit. But you had asked for SE operation in an earlier post, several alternatives were offered. This circuit does not fit SE from either the operation of the tubes or OPT.
So I’ll ask the obvious, have you done any tests on your PT to check if it is able to supply the power the circuit will need? The PT may have been discarded because it is defective.
Another point has to do with the B+, under normal conditions the resulting voltage of a FW, cap input PS usually falls in the range 1.2 to 1.3 times the supply RMS. That would get you a B+ in the range 350 - 375 Volts. The upper limit is set by the PT impedance & no further increase in the size of the cap will change that. 405V is the peak voltage, only at no load.
Finding a suitable OPT without the need to have one specially built will be a problem. A line transformer might do tho. 70V into One K is just under 5W. But line transformers are normally public address quality.
To get this circuit running you will need a good scope. Perhaps I’m telling you what you already know, in which case please excuse. I’ll be watching with interest as you sim the cct. 🙂
The PT was pulled from a piece of working HP test equipment years ago, so I have confidence in it.
The reason I was interested in an OTL design at the outset was to avoid the problem of my thinking I didn't have any, although I subsequently found these Fender 3W units that may work, in a pinch. If they do, then I suppose I could invest in some more suitable units.
I have about six scopes (my weakness), ranging from vintage Tek units to a modern Rigol 4 channel unit, and plenty of test equipment like signal generators etc..
I've transcribed the circuit into LTSpice, but it's having difficulty simulating it, which probably means I've screwed up somewhere. I need to check it carefully, but here it is:
I've assumed that ECC81 is equivalent to 12AT7, and ECC82 to 12AU7. The "trimpots" are shorthand for the pots in Ketje's schematic (which I assume are bias adjustment, but I confess to not fully understanding the circuit yet!). I may remove the NFB connection just to get the sim running - that could be the cause of Spice having hard time with the simulation.
Yes, ECC and AT/AU are the same thing. If you think the ECC82 is runing to hot (2W dissipated with Pmax= 2,75W) a ECC99 (Pmax=5W) is a drop-in replacement without mods.
There are two wrong values in my schematic, but no reason for not working.
By making a decent drawing on the computer I often do a copy/paste of parts to use them again.
In two places I forgot to adapt the values after reuse. C8 not 2µ2 but 100µ and R16 not 33k but 1k2.
Mona
There are two wrong values in my schematic, but no reason for not working.
By making a decent drawing on the computer I often do a copy/paste of parts to use them again.
In two places I forgot to adapt the values after reuse. C8 not 2µ2 but 100µ and R16 not 33k but 1k2.
Mona
If you drop the ASC file here, with any INC files it references, I have found some of the TSpce experts here on this site to be invaluable to highlighting my mis-thinking!
