Voice of Music 815: 6v6 Push Pull amp.

[wparks]

ahhh-ha. sorry i failed to mention that. i didnt power the pre-amp on while it was on the DBT, so im hoping nothing was shorted.
so basically i need to connect the blue secondary in between the black lead from pin 10, and pin 10. and if the filament is too high, reverse the blue leads.

i also realized, there is this (i think) wirewound resistor connecting pin 5 & 8 on the rectifier tube: it says "ohmite 150" on it. measures at 156.7 ohms. this is not in the schematic, but it would be sitting at the junction dot between the yellow 5v secondary & C1/R5. is this being used to choke the power supply?

Yes- that looks to be a B+ dropping resistor, just to lower the B+ voltage, probably a late production change. If it had a capacitor at the rectifier side it would add extra filtering, but as is it's just for dropping.

You may not need it, but I would leave it until you get the beast up and running and see where your voltages land.

 

[HepGreg]

alright! fixed the buck routing, hooked everything back up. passed the dim bulb test. turned on, no squawking oscillation! hooked up my ipod, and shes singing
sounds good, but a bit underwhelming. pretty sure the (basically) open baffle design of this cabinet is to blame for that.

for checking voltages itll have to be hooked up to the cab. should i pull the tubes & check voltages at the pin sockets?

now i need to sort out the turntable issues. if i cant figure that out, she'll be getting gutted most likely.

 

[gadget73]

need all the tubes in to get meaningful voltage readings

 

[HepGreg]

ah yeah. forgot about that.. i guess i can flip it over in the cab and put it on some blocks or something.

 

[gadget73]

if you can find them, these things exist but people tend to want a small fortune for them



can be had in all of the usual tube socket configurations too. At least I've seen them in everything from 7 to 12 pin. I haven't run into a set for the fat pin pre-war types but that doesn't mean they don't exist. I have a set but honestly I don't use them all that often. Most of the time its easier to just get the readings from underneath but some things are so densely packed or the chassis is such that there isn't any practical way of standing it up on its side for access.

 

[HepGreg]

@gadget73 oh yeah, ive seen those before. dunno if i can justify spending on one just yet.. this amp chassis is pretty spacious though. i cleaned up the wiring a bit as well, and ive got clip-on leads for my meters, so i should be able to do some easy, hands free readings.

replaced the last of the resistors last night, all the ones connected to the multican:

 

[gadget73]

I got all of mine at not-dumb prices, picked up here and there out of the "anything in the box is a dollar" type things or given to me with boxes of random old stuff. I wouldn't pay the prices people normally want for them.

 

[HepGreg]

got a new multican capacitor in from Hayseed Hamfest. got me leaning towards turning this into a standalone amplifier.


been pondering the layout, thinking about where i would put the additional 12ax7 socket. thought about changing the location of the can cap, but i realized the most logical course of action would be to move the RCA jacks & use the existing rivet holes to mount the tube socket, keeping the tube away from any power supply stuff. so i think thats what im going to do.

also found a perfect piece of wood at a construction site near my house, and fashioned some frame bits:

cut & sanded them, stained with india ink & sealed with shellac.

 

[opnly bafld]

I added new RCA inputs to my Magnavox because I only had one pair of wires that would kind of work (not really) with the original inputs.



I bought one of these VOM amplifiers off of Ebay a while back, but ended up cancelling the purchase after I found it needed the preamp to work without mods, the seller was not including the preamp and had misrepresented it in his ad.
Glad to see you are taking on the project.

 

[HepGreg]

I added new RCA inputs to my Magnavox because I only had one pair of wires that would kind of work (not really) with the original inputs.

View attachment 3737490

this is likely what ill do as well, but i think mine will go on the empty panel next to the power transformer. i also thought about just hardwiring in a 6 foot RCA cable instead of using jacks. still debating that.

 

[opnly bafld]

I like moving things around from time to time so the easier it is to hook everything up and disconnect it is better for me.
Tried keeping the 3 screw speaker connection too, but eventually put binding posts in their place.

 

[HepGreg]

I like moving things around from time to time so the easier it is to hook everything up and disconnect it is better for me.
Tried keeping the 3 screw speaker connection too, but eventually put binding posts in their place.

my maggie build was an 8600 chassis. it had the worst speaker terminals ever, i replaced with binding posts. this one has these weird little 2 prong plugs for the speakers, ill probably replace them though. its got 2 sets of speaker terminals though, which is kind of cool.

 

[wparks]

One solution I will suggest in remodeling these original style inputs- I unsoldered the original input connector, soldered in a patch plate, and drilled it to fit these small style RCA connectors. This only works if you don't mind grounding them to the chassis, but now they fit all but the fattest RCA cables and still looks original.

 

[wparks]

Hey- here is a thought- What if you put the new Hayseed capacitor in the hole where the big connector socket next to the rectifier, and put an octal socket where the can capacitor is now for a 6SN7 dual phase inverter. That would keep the bypass caps next to the power supply, and the phase inverters next to the pre-amp tube.

 

[HepGreg]

Hey- here is a thought- What if you put the new Hayseed capacitor in the hole where the big connector socket next to the rectifier, and put an octal socket where the can capacitor is now for a 6SN7 dual phase inverter. That would keep the bypass caps next to the power supply, and the phase inverters next to the pre-amp tube.

i thought about putting the hayseed cap there, but i dont think the hole is big enough. i would have to make it bigger. and then the original hole where the can cap is now, would be too big for an octal socket. which is why i arrived on the idea of adding the 12ax7 where the RCAs are, since that would require the least amount of modification to the chassis.

 

[gadget73]

One solution I will suggest in remodeling these original style inputs- I unsoldered the original input connector, soldered in a patch plate, and drilled it to fit these small style RCA connectors. This only works if you don't mind grounding them to the chassis, but now they fit all but the fattest RCA cables and still looks original.

View attachment 3737555

You can do similar without grounding them to the chassis. Phenolic board, and space them 9/16" apart. Its just enough to give you clearance on most cables, but not quite so much that it will touch the chassis. Stock the spacing is slightly under 1/2".

or you can buy that pre-made for a Dyna ST70 but I made my own for two different amps.

 

[HepGreg]

can cap swap went pretty smoothly.

 

[gadget73]

Thats the single best part about using a can made to the original specs. it just goes in and the wiring is cake.

 

[Dswankey]

Just clean up that chassis and you'll have a nice looking conversation piece amp.

 

[HepGreg]

Just clean up that chassis and you'll have a nice looking conversation piece amp.

i kind of like a bit of patina on the chassis, give it some character.

i pulled the V-M badge & indicator jewel out of the cab, mounted them on the front panel. mounted the light inside the chassis. need to wire up the bulb, will sort that out at some point.