A few details:
B+ = 470V, G2 = 125V, pretty close to the published operating point for the 815 in AB2, about 22mA per plate at idle. ~8k plate-to-plate load (using a 4.3k xfmr with 8 ohms on the 4 ohm tap).
The driver is simple, a gain stage and a diff amp, a resistor tail to a -95V bias supply.
There is global feedback from the OPT secondary to the cathode of the input tube.
Freq response using a Dynaclone A431S is down 0.05dB @ 20Hz and 0.02dB @ 20kHz, -3dB @ 75kHz (at 1W). Zo ~ 1.6 ohms.
Pete
B+ = 470V, G2 = 125V, pretty close to the published operating point for the 815 in AB2, about 22mA per plate at idle. ~8k plate-to-plate load (using a 4.3k xfmr with 8 ohms on the 4 ohm tap).
The driver is simple, a gain stage and a diff amp, a resistor tail to a -95V bias supply.
There is global feedback from the OPT secondary to the cathode of the input tube.
Freq response using a Dynaclone A431S is down 0.05dB @ 20Hz and 0.02dB @ 20kHz, -3dB @ 75kHz (at 1W). Zo ~ 1.6 ohms.
Pete
Cool, thanks for the numbers and other details, and web pages. Lots for me to learn from and get my 815s cranking. The bit with 8 ohms on the 4 ohm tap to double output resistance is new to me, interesting approach.
Garth
Garth
I have a couple of those. I have been thinking of trying a stereo approach with a 6SL7 as the driver. Neat!
Pete it looks like the modifications you made to the current board should be pretty easy to implement on the boards you so generously given to the members of the board. I am excited to see if these take off like the DCPP did!
I hope this isn't a stupid question but what is that green wire going to the 4 diodes and a bolt in the chassis right next to what I would assume is your normal ground?
That is where the circuit ground meets the chassis/earth ground. The diodes are for breaking potential ground loops, I believe.
Yes, there is a "ground breaker" consisting of 2 series back-to-back silicon diodes between ground and chassis / AC line ground.
There is also one little error that I fixed after taking the photo. The green wire headed to the power transformer is the filament CT. In the photo it is connected to chassis / AC line ground - it is supposed to be connected to ground, not the chassis.
Pete
There is also one little error that I fixed after taking the photo. The green wire headed to the power transformer is the filament CT. In the photo it is connected to chassis / AC line ground - it is supposed to be connected to ground, not the chassis.
Pete
Well, sure but where I come from I cannot get a hold of the exact components used by Pete and I would like to be faithful as possible to the original design...
with an excel BOM I can order from Mouser and be sure to get the right parts (shipping and VAT are expensive here so if I order I need to be careful to get everything I need).
🙂
with an excel BOM I can order from Mouser and be sure to get the right parts (shipping and VAT are expensive here so if I order I need to be careful to get everything I need).
🙂
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