Deluxe Reverb RI bias question

[Newguy]

I did shunt method on BF Super Reverb a while back with help from this forum, seemed easier with point to point wiring.

I have BF Deluxe RI apart now. Trying to do shunt method. I just need ma reading so I can do calculations, as I have plate voltage at 430v right now.

1. I can get plate voltage pin3 (6v6) to chassis ground.
2. I need to get the bias ma reading, which I think is pin 3 of 6v6 (black dvm probe) to center tap of OT (red dvm probe). Research said center tap of OT transformer is red wire with yellow stripe ). The only red wire with yellow stripe I saw was connected to pc board CP9.

I put dvm to ma setting.
I powered up, then powered on stand by, seemed to be starting to get reading, then fuse on amp blew?

New fuse, and amp is working fine.

I do not know if I am doing something wrong, or if it was just a fluke that fuse blew. I had to put wire on CP9, then put connector back on, maybe it was not a good enough connection? I connected other end of wire to dvm red probe.

To get bias ma reading, am I putting meter probes in right places. Is there a better place to put probes IE test points, or another location?

I would prefer shunt method vs resister method if possible.

Please help..Thanks

[MWJB]

Red wire with yellow stripe is the POWER transformer centre tap, you need to use the output transformer centre tap which is plain red & enters the chassis with the blue & brown primary wires. You shorted the plate to ground, replace the tube.

[Newguy]

MWJB

Thanks. Big Thanks. I do not think it blew tube? I just plugged in and played, amp sounds fine. However I plan to order matched Tung Sol reissue's next week.

I am looking and I am not sure of the red wire primary you speak of. I see two red wires on rectifier tube socket, which I doubt is what you refer to. I see another location also.

I will post picture and put it in paint and circle the red wire I see.

The brown and blue wires you speak of, that is not the pin3 of each power tube is it, left tube pin 3 brown, right tube pin3 blue?

Glad amp blew fuse quicks. Could or should I have seen fireworks?

[MWJB]

"I am looking and I am not sure of the red wire primary you speak of." See CP14.

"The brown and blue wires you speak of, that is not the pin3 of each power tube is it, left tube pin 3 brown, right tube pin3 blue?" Yes, these wires are the "ends" of the OT primary winding, the red wire running to CP14 is the 3rd primary wire, AKA "centre tap". Look at the transformer drawing on the schematic, you'll see the red "B+" wire sits "centrally" between the windings connecting to the blue & brown wires.

"Glad amp blew fuse quicks. Could or should I have seen fireworks?" Sorry to dissapoint with the lack of fireworks, all that would happen with a shorted primary would be that the fuse would keep blowing & probably burn out the OT winding (but you wouldn't see this happen).

[jmaf]

Positive lead goes on RED, negative on any of the 6v6's pin3 (blue or brown wires?).

Edit: If in doubht, take it to a tech and pay a few bucks for a bias adjustment

[Newguy]

MWJB

Man, glad you are still on line. Big help man. I think you told me every thing I need to know with the location CP14.

Posting the few pics I took any way just for reference at another time. Hope file size is not too large.

Thanks MWJB have to go out but will post results later

[pontiacpete]

"The brown and blue wires you speak of, that is not the pin3 of each power tube is it, left tube pin 3 brown, right tube pin3 blue?"

yes, if you follow the brown and blue wires on the the 6v6s to where they come thru the chassis, you should also see a red wire, that is the one you want. You can check to see if that is correct with you meter set on ohms, measuring betw red-brown and red-blue will give you a resistance somewhere around 70-100 something ohms.

[MWJB]

That's what he said, he just had the wrong "CT".

[jmaf]

Yup. Realized it. If there was gum wrap or straight wire on the fuse box he'd have a mushroom cloud.

[MWJB]

Ha ha, had a client that tried that with a UL Twin, "The lights dimmed, there was a hum & a puff of smoke and the AC plug got spat out of the wall socket"...PT, OT, rectifier all dead! :-(

[Newguy]

LOL guys.

I have to get ready to leave.

Tried the ma reading, I am getting 16.60-16.70 ma. (on left v6v6 tube looking from back..brown wire to red wire).

I have plate voltage (6v6 pin3 to chassis ground) set at 435.

435 x .017 = 7.395 watts.

That does not seem correct but have no time to look it up. Amp sounds fine.

I am starting to wonder if I have a 6v6 or 6v6 GT tube in it. Yea, I know I should have 6v6gt in amp. I do not see markings on tube but was in a 6v6 box. Not sure what amp it came out of as all my stuff is so old.

Amp sounds great but hate to even leave house as I would like to know what I have done lol.

PS Thought it was strange, had guitar still plugged in (forgot). Any way, no sound from guitar when meter is hooked up. Un hook meter and get guitar sound? I think you are not supposed to have guitar hooked up for ma reading, but thought it strange that getting reading from tube (ma) and no sound when meter connected.

[jmaf]

Ha ha, had a client that tried that with a UL Twin, "The lights dimmed, there was a hum & a puff of smoke and the AC plug got spat out of the wall socket"...PT, OT, rectifier all dead! :-(

Hihiii... OT PT grand slam... To do "better" than that, he'd need a flamethrower.

Last week I was messing with a friend's JCM 900 head he had brought for me to have a look at, it was working fine, just new tubes. So I poked around looking for the usual stuff and found all fuses were direct wires, all of them, the two HT power valve fuses and the mains.

[MWJB]

Are the left & right 6V6 matched (+/-5mA)?

"That does not seem correct but have no time to look it up. Amp sounds fine." If the amp really sounds fine, then it IS correct. However, most old/NOS 6V6 don't tend to like plate & screen voltages above 425vdc, modern 6V6 (typically all 14W GT rated) don't mind the higher voltages. If you want to stick with the NOS try bumping up the current until the plate voltage comes down...then have another listen.

You can't play your guitar when the OT is being shunted, if you want to play whilst setting bias buy some bias probes.

[Newguy]

With those readings it must be 6v6 tubes and not a 6v6gt right?

Man, I love the way the amp sounds though?

I will have to search over current tubes with magnifying glass later, as my eyesight is terrible, maybe there are some markings some where.

If that is a 6v6 tube, that would be WAY too high plate voltage correct?

I do not see any thing out of the ordinary when playing and looking at tubes from the back, and amp does not appear to be running hot, nor have any strange noises?

Later Guys

[MWJB]

"With those readings it must be 6v6 tubes and not a 6v6gt right?" Why? There's no reason why a 6V6 should specifically idle cooler than a 6V6GT...in all likelyhood it probably is a "GT". People tend not to bother distinguishing between 6V6 & 6V6GT these days as 6V6s have been GT spec since 1940.