I use SMPS for 12V heaters all the time. I always rate them for twice the nominal heater current and pick ones that have hiccup mode. This way I find I can guarantee they will fire up into cold heaters. In this particular case we have two SMPS in series; the AC/DC one in the wall wart and the DC/DC that produces HT and 6.3V. The 6.3V output is rated at 1.5 amps but I found it will only fire up into a single cold 300mA heater (ECC88). I suspect the problem is the wall wart is rated at 1 amp and is being asked for current pulses much bigger than that. What I will do is monitor the wall wart output to see if it goes into current limit with cold heaters.
Thanks for the links. I ordered one of each. I like the through hole one because it seems to have an extra filter stage (as shown in the chip datasheet) which drops the ripple a lot but it will still need some more RC smoothing after that to get the ripple down to levels acceptable for audio use.
I am not familiar with the Tele V. Do you have a schematic you could share?
Judging by the number of tube tone boxes I have built for people, whatever it does, the SRPP sound is well liked. The guy who purchased my very first tube mixer which uses 6CG7 mu followers throughout, uses it to process and mix three final stereo stems.
The mu follower is intrinsically a gain stage plus a cathode follower, so it would make more sense to use a gain stage plus cathode follower in cascade, since you are voltage limited not current limited in this case.
Except you lose the inherently low distortion of the mu follower and replace it with the regular CC stage distortion plus you probably double the HT supply current requirement but you are right, it will have a better voltage swing.
Not if you bootstrap the gain stage anode resistor -it's literally the same circuit laid out horizontally rather than vertically. Current doesn't need to double since you have the freedom to run the gain stage at low current. Anyway I thought tube character was the whole point of this DI?
Bootstrapping the first stage plate will certainly help a lot. I agree you could run the first stage at lower current but then you very quickly run into grid current problems.
Yes, I agree. I think a 1Meg pot at the input and a 1K pot on the output will provide drive and output controls and allow people to experiment with the sound.
I had fun trying this out. The only suitable transformer I had to hand was a line input transformer from a 1073 (configured for a 2:1 step down). It is too small for this job really, i.e. copper losses and it saturates below 30Hz at 5Vrms output, but it scrapes by as a proof of concept. Frequency response shown, and distortion at 1kHz, with a 600 ohm load. Output resistance was measured as 370 ohms, about two thirds of which comes from the transformer winding resistance.If WCF is being considered then this seems like a good time to revisit the cathodyne unity-gain line driver
https://groupdiy.com/threads/cathodyne-mu-follower-line-out.86934/post-1139274
