Power Supply Question...

[v00d00blues79]

I'm in the process of putting together my next build and i have a few questions regarding the differences in the power supplies between the '97 schem and the Hybrid-A. The '97 schem shows the resistors as 3k, 12k, and 10k. This has the B+3,4,5 set at 433, 361, and 323 vdc respectively. Now on the Hybrid-A schem the ps resistors are 2k,22k(27k), and 1k(2.2k). This has the voltage readings at 436, 306, 303vdc. Thats a pretty sizable difference in voltages between the two. My question is how will this affect the tone of the pre-amp? My gut tells me that it will stiffen up the pre-amp a bit, but i very well could be wrong. My amp is going to be using the '97 PS (its hard to pass up on .96c per cap) and the Hybrid-A pre-amp. I know some of you had to have tried this combo before and am looking for any suggestions.


Thanks,

andy

[dogears]

Andy,

None of this matters. The voltages are based on what the PS is putting out. THe dropping string is only a means to an end.

Try experimenting. Listen to the differences between 200v on the preamp tubes and 220v. Set where you like. Mine are usually between 200v and 210v.

Also, keep in mind that Dumble had a FET that was loading down the last dropping resistor. Try hanging a 150k to 180k to ground from that point. Otherwise, your preamp plates will be running a bit more V than intended.

[dobbhill]

FYI-the voltages on the "Skyline" schematic in the files section are from an actual ODS. They have been a very good guide for my builds in the past.
HTH,
D

[v00d00blues79]

Sweet. I figured as much, but there is so much to these amps that are affected by voltage variations and one section impacting another that i wanted to make sure. Also, i went with the Xicon MPP's and the OD 225P's for the pre-amp. The Xicons are tiny compared the OD's... I just thought of another question... if i choose to omit the mid-boost function in this amp would i be able to omit the mid-boost cap from the circuit? what is everyones thoughts on the mid-boost? is it a necessity to get the tone?

Thanks,

Andy

[dogears]

True... But, where you aware that there are bad mistakes on those schematics? The 1997 HRM amp that was degooped and that the schematic was based on had a 500pf treble cap in the post OD stack and not 330pf. There are various "liberties" that are taken on them as well.

In addition, having a FET loading things down, does dramatically alter the B+ to V1 and V2. I know for a fact that there are people that copied the schematic and did not use a FET. Their B+ was way high. After adding the simulated load, the tone got MUCH better. Just ask Funkilicious Groove!!!

Don't get me started on Hybrid A with its 330k series resistor feeding the OD level pot!!! LOL

FYI-the voltages on the "Skyline" schematic in the files section are from an actual ODS. They have been a very good guide for my builds in the past.
HTH,
D

[dobbhill]

I remember when that "set" of schematics was being "assembled". Some parts values were measured, and lots were guessed and assumed. I am fortunate to know which were actually measured, but more fortunate to have you in the forum to point out the mistakes. I manipulated the B+ dropping resistors to get the proper plate voltages, but I just might try the "simulated FET circuit" you recommended. Let me know when you can release the de-gooped data........
Thanks, D