JE Labs 300b round 4. Wiring, HELP!!!

[fdegrove]

FINISH IN SIGHT.

Hi,

Are the centers of RCA jacks posistive connection?

Yes.

Also, my OPT has multiple leads that you connect in certain combinations to achieve the required ohms for output. I have two leads left for the binding posts.

Assuming 8 Ohm speakers you connect the 4 Ohm to the 8 Ohm and this then receives you + binding post (red).

The 16 Ohm is not used.

The - terminal only recieves a binding post (black) and needs to go to chassis ground.
Usually that wire goes to the grounding point closest to the input.

The attenuator needs to be wired. there are three holes labeled " in / out / grnd " Now the 'in' wire is from the RCA? the " out" wire to grid of first signal tube? ground goes to ground. This would put the attenuator in series with the signal coming into the amp?

Correct.

Would it hurt anything to wire up the hum pot? or will the hum pot not work with a DC filament? I know it adds to the signal path but want to try the hum pot if I can use it.

It could still be used to balance the heater voltage in case it would have uneven internal resistance causing hotspots on the cathode.
This sometimes happens with tubes but here it is only useful if you have the necessary equipment to set it correctly.
It will have to be readjusted every time you change the output tubes.
Also keep in mind that the legs of the trimpot are in essence part of the cathode resistor so you better wire it in and set it so that both legs show equal resistance from the wiper point.

What should I double check, besides everything, before pluging the amp into the wall socket and throwing the amp switch closed( WITH A LONG BROOM HANDLE )?

LOL.

Try to get hold of a variac (or someone that has one) so you can bring the voltage up gradually.

so everyone can take a look to spot anything I might have overlooked.

I have nothing against it.
If you have a friend technician that would be a bigger help.
Before you fire it up check for obvious wiring mistakes on the tube sockets and see that all soldering is valid.

Good luck,

 

[TubeHound]

Hi Frank,

Thanks for checking this thread all the time, I do appreciate it.

here it is only useful if you have the necessary equipment to set it correctly.

Could an oscilloscope be used to set the voltages on the 300b heater wires?

I did discover, by double checking, that I might have made a mistake in the building of the 300b filament rectifier circuit. I had bolted the diodes onto the heatsinks back to back, shorting the positive leads together. They should be seperated to operate correctly. For now I have taken the heatsinks off and seperated the schottky diodes. I believe there will be about 10 watts dissipated on the diodes combined. I am hoping the diodes can withstand this heat without the sinks attached.

Waiting for one more part to arrive and then it's done. I overlooked ordering the 22uF 500v cap at the end of the 6sn7 plate circuit. This must be divine intervention

 

[dhaen]

I am hoping the diodes can withstand this heat without the sinks attached

2 Watts? I say no.

If you remember, in an earlier post, I suggested bolting them to the chassis using a suitable insulaton kit
Why not buy some insulation kits? Then, the world is your oyster

 

[fdegrove]

SCARY DIODES.

Hi,

Being myself..frankly I don't like these much.

Paul,you could also mount then upright on a mounting boards and attach heatsinks to the buggers.

If you wired as I suggested you would have at least one board to spare anyway.

Than mount a little heatsink to each making sure they don't touch anything else.

Or you can go for John's OysterCult.

Cheers,

 

[dhaen]

Schottkey is magic!

The technology didn't get us to the moon - that was CMOS
But it was a stepping stone. And now it's helping us with something simple like rectification - theres something nice about that.

 

[fdegrove]

DIDN'T GET IT DID YOU?

Hi,

Or you can go for John's OysterCult.

Better watch out!

Cheers,

 

[dhaen]

Frank, I swear you're getting worse

 

[TubeHound]

Hi,

I plugged the amp in to the wall socket. Here is what happened

1. My ON light lit when I plugged the power in and turned off when I closed the main power toggle. Easy fix.

2. No heater voltage for the 300b. All other tubes glowed. Checked rectifier circuit, noticed there was no solder connecting the rectifier circuit to the a/c lines coming in. Fixed that.

3. Not sure, if the GZ37 is wired correctly. The filament glows. I took the B+ off from pin 8 of the octal socket to the first cap. I noticed that the pinout for the GZ37(CV378) shows:
1= Shell, what is this?
2=H, heater
3=n/c
4=a, plate, wired the 380v from tranny
5=n/c
6=a, plate, wired other 380v
7=n/c
8=H+k, heater, wire to first cap, B+

Anyway, disconnected the power cord, waited 5 minutes and checked caps with DVM, no volts showing.

Thats it,

 

[dhaen]

1) Is an internal connection, leave alone.
Other pins sound as if you've connected them properly.

What you haven't said is whether you measured +B when it was running. And whether you put any audio through.

Cheers,

 

[wopontour]

300B DX

Hello Paul
I see you have long since completed this JEL 300DX
I'm building a stereo version of the same (not mono blocks)

Q: Did you use the JE reccommended quad of 47 mfd filter caps?
and if so, did you find the plate transformer ran extremely HOT?

Also, the "Stereo DX" schematic alters the 300B cathde resitor from the monoblock value of 880 ohms to 900 ohms on the DX. In light of the LOWER supply voltage of the DX (390V vs 405V) doesn't that seem backwards? Does change have more to do with the OPT selection?? (I'm using Hammond 1627SE)

Thanks for your (or anyone's) assistance

Regards
Alan