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I have read that this can be a nice sounding SE amp. I have pretty much everything I need to make the amp except the output trans. I am thinking of getting the Hammond 30 watt 10K primary units mostly because they are not super expensive and since I am going to be "massaging" the circuit I don't want to commit to very expensive outputs at this point. I just wanted to have some feedback by anyone out there who have more experience with what is required for a SE output trans with this output tube. Thank you for contributing to my education. Dak
Fortunately the triode curves are available. Draw out a series of different operating points at different impedances to make your decision.
Hi, Palustris and thank you for the link to the discussion on the 813 tube. This is very much what I need to develop my circuit. I shall endeavor to keep you all abreast of my progress. It seems like the Hammond OPT is a good starting point for my project. I am thinking about 30 watts of power per channel is plenty for Altec 19 speakers. cheers, dak
FWIW, those transformers won't produce anything like 30W at the lowest octave. The Hammond frequency response graph (which is already down > 1dB at 20 Hz) was produced at an equivalent output power level on the order of a few mW. Based on their size, it's likely these transformers will saturate around 6W to 7W at the lowest frequency. That may or may not be sufficient for the Altecs. Just wanted to point this out as something to consider before you start your project.
Ok, so, if the B+ voltage is made lower to limit output power that could help ?
Yes, lower B+ will reduce power across the entire spectrum. FWIW, the Magnequest FS-100 transformers in my 211 SETs behave the same way (also rated 30W). If the severe reduction in output power at 20Hz were used as the baseline, a 300B could do as well with OPTs this physical size.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Hey Tre, thank you for posting the graph. It seems to indicate that maybe a worthwhile project for hopefully develop a nice sounding amp.
If you can bring yourself to try PP, a 600V/100mA idle point with a 10k a-a load( Peerless S-265-Q ) does pretty well too. I did this with a pre-existing amp that ran them with 20% U-L. Had to try the triode connection... :) Went back to E-Linear NFB, and then back to the previous power tubes( 4E27 ).
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Hi Pak and thanks for the recommendation. I do not need the power that would use PP 813 amp. Part of the appeal for me using the 813 tube is how it looks when operating and from what I have read also sounds good too. I have made and listened to many PP amps and after trying single ended amps, I prefer the audio experience from SE.
Looks pretty linear, even at lower voltages. Would love to see this on a curve tracer.
The big issue with such an amp is safety though. Read up a lot on safety and high voltages.
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