Pilfering parts for a build, and a few questions.

[FE911]

Being a little miserly at times has produced good results, sometimes bad. I've gone the high-dollar route on a few builds with both good and bad results. Now I'm going back to pilfering for a build on this one. I've got an old Harmon Kardon (mid-fifties) mono reciever that I want to build into a 18watt Marshall. I haven't decided on what favor yet, but I haven't done a TMB yet, so I'm leaning in that general direction. So many twists to choose from!!!!
The HK chassis is an old copper number with 13 total tubes, it has the gz81 and two el84's. The problem is there are two filament windings coming off the xfomer. One is marked 6.1 for tuner filaments, and 6 (with center tap)for amplifier filaments. The 6 volt filaments have a "Hum adjust" on the schematic, which I'm not familiar with. My plan was originally to use the 6 volt filaments for all tubes and scrap the standby switch. But are the 6.1 filaments that run the tuner tubes(eight total) suitable for the el84's and preamp tubes? Is there an easy way to figure out the amperage for the filaments? This would allow me to use the 6 volt with center tap for just the gz81 and have a standby switch. Thanks again!

[CaseyJones]

My Harmon Kardon is close to yours I think. Mine has around 12 volts on the preamp filament winding and it's rectified for DC filaments. The OT feeds two Quam 12" speakers (plus passive crossovers and some HF junk) for a total speaker load of 4 ohms. Between the oddball PT and the oddball OT I decided to save that one for a rainy day and work with somethng else.

It's sacrilege to cut up an old Pilot Radio or Fischer but man thay have nice OTs tapped for 4, 8 and 16 ohms. I have an old Fischer integrated amp that used 7591s, not exactly what you need for your project but you should see the output transformers!

That one looks like it fell off a truck so I don't have even a twinge of guilt about hacking it up.

[b24warbaby]

Is there an easy way to figure out the amperage for the filaments? This would allow me to use the 6 volt with center tap for just the gz81 and have a standby switch. Thanks again!

You gota have a RCA tube book by now .. Right ?

Do you know the tube inventory of the HK ?
sum up the filiment amperage on the tube run
and that will give you an idea of what
you have.

A hum control is simply that. It adjusts the heater voltage
across the center tap winding to be symmetrical to eliminate 60z hum.

[benoit]

Is there an easy way to figure out the amperage for the filaments? This would allow me to use the 6 volt with center tap for just the gz81 and have a standby switch. Thanks again!

You gota have a RCA tube book by now .. Right ?

Do you know the tube inventory of the HK ?
sum up the filiment amperage on the tube run
and that will give you an idea of what
you have.

What warbaby said. Each tube type has a pretty dependable heater current draw. 12ax7s are around 300ma each (both sides, or 150 per side), el84s are 760ma per tube. I'm guessing if you had 13 tubes in there the heater winding should easily be able to meet the demands of an 18 Watt TMB.