Other Amps

I’m rebuilding my 6g15 reissue…

51

Thanks. Yeah. That's the plan.

There is plenty of clearance on the lead-ends of the caps, but the tops of the caps might hit the roof of the doghouse. This is not a problem, right? I'm planning on putting a bit of foam on the inner "roof" anyway.

52

Yeah,that'll be fine.I used that double stick foam tape.Just leave the paper layer so it only sticks on one side.Its nice and thin but will still give that extra measure of support so the can wont move when transporting the unit.Just so you know,the can itself,under that plastic shrink label,is grounded anyway,so even if the plastic was somehow removed or,as I've done myself,you accidentaly touch it with the iron,melting and exposing the can,it wont hurt if the metal can touches a ground.

53

Good to know on the grounded can.

I have some left over foam tape that I used at the bottom of a leaky window. It might be perfect for the job. Sticky only on one side.

54

So, I'm getting close to taking out the current guts. A few questions...

Seems to me that by looking at the schematic for the reissue and the original unit, the choke has two black wires. Does it matter which side the choke wires come from? Or is it not an issue which way it is fed from the rectifier board?

Same question for the heaters. Are both green wires from the transformer interchangeable? Can I send either one to the tip of the pilot and then just send that wire to the 2/3-4/3-4 and the other to the 7/9/9 pins?

Everything else is pretty clear, but the transformer wires are a bit confusing due to the duplicate colors. I'll be clearly marking the current connections with labels once I clip the plug ends and I'll send those to the same connections as on the RI.

For example CP-8 from the PT goes to the AC switch and CP-3 goes to the fuse. (these are the two black wires from the PT)

BUT!!!! CP-11 and CP-12 (the two RED wires from the PT) seem to be interchangeable?

55

So, I now know that the red and green secondaries are interchangeable. And the black primary goes to the fuse and the white primary goes to the switch. (the reissue transformer has black/white primaries unlike the original which had two blacks.)

56

Regarding the heater and primary connections, I have a couple suggestions. Assuming you're using a 3-prong plug, the best (safe) way to wire the power is to run the black wire of the power cord to the fuse first. Then from the other connection on the fuse jumper it over to one side of the power switch. Then one of the primary connections on the transformer gets wired to the other side of the switch, and the other primary on the transformer gets connected to the white wire of the power cord. Of course the green power wire gets grounded, preferrably at the transformer mounting bolt.

If you have a center tap on the secondary heater winding (usually a green/yellow wire that is grounded near the PT) and the traditional bayonet style pilot light I prefer to wire my heaters as follows. The 2 green secondary wires are twisted together and go to the 2 connections on the pilot light. Then you run another pair of twisted wires from the connections on the light on down to all of the filament connections on the tubes. The only thing to watch out for is keeping all of the tubes in phase with eachother. You can still do this without a center tap on the transformer, you'll just need to create an artificial center tap by installing a 100 ohm resistor from each connection on the pilot light to ground.

Aaron

57

Ok, I just zoomed in on the layout you posted above and noticed that the resistors drawn-in on the power tube are accomplishing the artificial center tap for the heaters. If your transformer has a center tap you won't need to do that part. Regardless, one wire off the pilot light will pick up pin 7 on the power tube and pins 4&5 of each preamp tube. The other wire from the light will pick up pin 2 on the power tube and pin 9 on each preamp tube. Keep the wires twisted together when running from tube to tube to keep down AC hum.

58

Aaronbrill. Thanks for the notes.

I have a couple questions. You say to wire the heaters 7/4&5/4&5 and 2/9/9.

On the reissue schematic, seen here:

the heaters go from 7/9/9 and 2/4&5/4&5

So, what exactly is the correct way to keep things "in phase".

I'm keeping the Reissue Power Transformer so it has no center tap, hence the 100r resistors on the 6K6.

And, finally... The wiring, would it be bad to wire the AC as seen in my layout? With the hot wire going to the fuse tip and then on to PT primary A, and the neutral wire going to the switch and then onto PT primary B. (and the green ground wire locking onto the chassis ground nut.)

60

Wire the heaters like you see in the re-issue schem,pin 2 to pins 4/5 and pin 7 to pin 9.Again the PT primary should be as you se in that schem.In that layout you have for the original you see the "artificial center tap",the two 100ohm resistors connected to the cathode of the power tube instead of ground.That is a technique used to reduce hum.It raises the ground potential of the ac heater supply by whatever the cathode voltage is,thereby keeping the current from the ac supply that much away from your signal ground.Very effective in a cathode biased amps.

61

stokes. Thanks. When you say "the PT primary should be as you se in that schem." which layout exactly, the one I posted right above your post (my own amended version of the original? or the reissue?

I've just finished desoldering all the connections on the tubes and I'm taking out all the PCBs. Desoldering with the plunger tool is pretty fun.

62

Wire the PT primary like the re-issue schem.Black to fuse,white to switch.

65

You're in the doghouse now...

66

Package is still on its way. Cleaned up power supply wiring a bit and soldered in the two 100 ohm resistors on my octal socket. And soldered up the OT leads to the RCA out. And crimped a nut mount collar on my rectifier ground.

Outlet works, and the PT fires up a-okay. Jewel lamp glows, just above 130vdc before the diodes on the rectifier and just over 250vdc after they pass through the rectifier. 8ish vac on the greens. 130vac on the primaries. Something like that. Once it's all wired up I'll photograph all the readings.

Jacks have resistors and are installed.

67

Just a suggestion.Those 100 ohm resistors look like 1 or 2 watters.It is better to go with 1/2 watt as they can act as a fuse if there is a problem with the heater circuit.

68

Interesting. I might have some 1/2 watters. you are correct. They are 1w resistors.

69

Wired up the heaters. They are pretty out of the way of everything this way. And, they work! I even dropped in some tubes and they warmed up to a nice, healthy orange glow.

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70

Man this thread is awesome. I just got one of these and I thought it might be fun to take on the same project this summer. Ill be following along diligently. Thanks for this!8-)

71

Thanks for watching Jay. I hope it turns out well. I'm getting close. Still waiting on the last batch of components. I'll be swapping in some new .1 coupling caps (maybe) and then wiring the main board in place, then... action! (then troubleshooting!!??)

72

Hey I am finding you on several forums with this you rascal..all of them informative from various agents piping in. good on ya.

73

If you dont have any 1/2 watters,I could send you a couple,it would be faster,assuming you are in Bklyn,than ordering them somewhere.I kinda want to see this project finished,its taking you forever! Just kidding.Send me a pm with your address if you need.

74

Hey. That's a really nice offer, but I had a couple 1/2 watts and just finished swapping them in.

Thanks a million anyway.

J

75

Tavo, yeah, I figured I'd cast a wide net since there are smart folks on all these forums...

New AC wiring... and 1/2 watters that I found at Leeds Audio... crusty bastards.


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