guavatone said:I’m not clear on your question. Switch is A,B and C. Position A bypasses PAD. B and C are -15 and -20 respectively.
Can you tell more about the DC heater setup? Transformer specs? Regulated? For regulated 6.3V you really need an 8-10V transformer.
6.3 x 1.414 = 8.9V leaving only 2.6V difference which a close margin for Regulators
I was doing some test in HD recording at 96K and didn't like the HF response. I found that the HF stuff was coming from the gain switch caps that cut HF by a boosted Negative Feedback high Frequency signal. when measured on the AP it sure enough showed jagged edges rather than a smooth rolloff. So rather than using Feedback to cut highs, we'd rather cut them a bit at the input. And at low feedback settings(higher gain) there was some HF loss. This is the nature of Negative feedback. When you add Negative feedback bandwidth increases. Remove Negative feedback the inverse occurs. So the cap across R8 is to compensate for this. Shall we call it a compensation cap? So with the 22p-33p cap across R8 with the Constant Impedance Gain Switch, we get fairy flat response to 20K. And with the High cut at V1's input we get lest phasing from the old gain switch. By "K (4^5)" do u mean KiloVolts?iomegaman said:Hey just another meandering question:
I notice in picture of the "mod" where you install a couple of caps across V1 grid/R8 mod that there is another cap across :
V1 K (4^5)
...what are you running there and why? Is that for noise or oscillation? Looks like a high frequency cap of some sort?
guavatone said:It’s really not a good idea to test without tubes in because some parts rely on the load to have correct voltages. Check your cathode circuitry. Is seems like your tubes are not pulling a load on the ef86 and E88cc.
Are you using 2 high voltage power supplies?
Are there any resistors in the heater supply path? Are you testing with only one channel hooked up at a time? It doesn’t make sense that your heaters could show 4.4 and 6.6 V at the same time
guavatone said:All your measurements seem to be referenced from ground to the pin right?
When measuring heaters pins 4 and 5 just measure the voltage between the 2 pins and not to ground. The heater is quite low. And most likely throwing off other operation point voltages.
What do you get between pins 4 and 5?