Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shooter on February 18, 2018, 03:27:41 pm

Title: can't figure it out
Post by: shooter on February 18, 2018, 03:27:41 pm: 'm ooglin schematics for my next build and I find this;

I'm looking at V1b :dontknow:
my guess is it's common grid :dontknow:, some sort of AGC :dontknow:
Title: Re: can't figure it out
Post by: kagliostro on February 18, 2018, 04:17:07 pm: Also the OT winding at cathode is a bit odd to me
not the winding at cathode itself, but the intake that goes to pin number 5 of the connector .... :w2:

Franco
Title: Re: can't figure it out
Post by: VMS on February 18, 2018, 04:23:37 pm: Some kind of voltage regulator maybe :dontknow:
Title: Re: can't figure it out
Post by: shooter on February 18, 2018, 04:52:14 pm: Quote
Also the OT winding at cathode is a bit odd to me
If you look at the legend, they use that as the 70.7v type line out, inductors were once considered cool :laugh:

I'm really only interested in a V1 phono preamp circuit that's odd :icon_biggrin:
Title: Re: can't figure it out
Post by: shooter on February 18, 2018, 05:25:58 pm: :BangHead: I'm even more confused, I can't get B+ to V1a :think1:
I'm now leaning to some sort of PI???, I'm redrawing it so I can see better :dontknow:
Title: Re: can't figure it out
Post by: sluckey on February 18, 2018, 05:41:06 pm: V1A plate current path flows through R8 to V1B cathode to V1B plate to C12C.
Title: Re: can't figure it out
Post by: VMS on February 18, 2018, 05:53:49 pm: It's a voltage regulator, look at the schematic on this service manual:

http://www.vintagevacuumaudio.com/schematics-manuals/mcintosh/mcintosh-mc60-service-manual-parts-list-schematics.pdf (http://www.vintagevacuumaudio.com/schematics-manuals/mcintosh/mcintosh-mc60-service-manual-parts-list-schematics.pdf)
Title: Re: can't figure it out
Post by: shooter on February 18, 2018, 06:04:09 pm: You folks are amazing, thanks

I also just sorta skipped over the "preamp" part of the connector and read "input" :think1:

I found the revised schematic that eliminates the neon's, then found type 125 that eliminates the regulator :think1:
Title: Re: can't figure it out
Post by: shooter on February 18, 2018, 06:54:08 pm: ok, think I get it, maybe. I redrew V1, if I tweak R5/R31, I change V1a's plate voltage?

Is there something I'm missing if I feed my own "next" gain stage? can I keep it DC coupled? or is it better to cap couple? I'm going for SE vs the PP
Title: Re: can't figure it out
Post by: PRR on February 18, 2018, 08:35:09 pm: > SE vs the PP

??

Anyway--- That's a McIntosh. Mere Mortals are not supposed to understand. The killer detail is the unity-coupled OT, something NO other maker ever attempted. The flip-side is that it needs HUGE signal at 6550 grids. McIntosh was full of too-clever ideas. To sell them, he put every bell and whistle on. Great amps, but not for you.

That's not a suitable steal-point for a guitar amp.
Title: Re: can't figure it out
Post by: shooter on February 18, 2018, 09:05:35 pm: Quote
That's not a suitable steal-point for a guitar amp.
this idea is a mono-block 10-20W. I want a phono level in and something that can deal with 1-2vac in. It's more about "that's unique", also, can I make it variable, if so, I can scope the effect of changing DC plate, on AC signal :dontknow:

I also found a meter circuit from one of my early hero's, Mr. Mims
Title: Re: can't figure it out
Post by: shooter on February 19, 2018, 08:02:20 pm: here's the 1st draft pre-section. the PA will be one I used before, QSE EL84's
not all the values are there yet, any that are, I'm open to recommendations

I named it, now I gotta build it, slowly, probably start with a new BB rev 3 :icon_biggrin:
Title: Re: can't figure it out
Post by: shooter on February 20, 2018, 11:57:46 am: It's 62degrees!!! so I tore down the donor chassis.
3.5kw mod-sinewave invertor that I, um, forgot to switch out when the grid came back :cussing:
Title: prune 5.6
Post by: shooter on February 23, 2018, 04:28:55 pm: finally found all the Iron :think1:
250v 200mA PS
10H 200mA choke
25W UL OT

now I need casters :BangHead:
Title: Re: prune 5.6
Post by: Willabe on February 24, 2018, 11:23:05 am: Quote from: shooter on February 23, 2018, 04:28:55 pm
finally found all the Iron :think1:
250v 200mA PS
10H 200mA choke
25W UL OT

now I need casters :BangHead:

:laugh:
Title: Re: can't figure it out
Post by: shooter on February 24, 2018, 11:48:08 am: I bread boarded the panel meter last night, probably have a switch to monitor input, or output of the preamp.
Title: Re: can't figure it out
Post by: shooter on February 27, 2018, 09:40:28 pm: got 2 many fires going so I took the Hammond 270HX and plugged it in, PT test into a 5K load gets 408vdc with a fullwave, ct grd. I haven't had an amp since Christmas, :sad2:, and I'm not even a player :think1:
hopefully by the weekend