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Post subject: Help: Puzzling Issue with a '66 BFDR
Posted: Sun Mar 27, 2011 8:27 pm
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I'm having a puzzling issue with my '66 BFDR. Last month, after putting the amp on standby for about a half-hour, and then returning to play again, I quickly noticed that I wasn't able to obtain much volume, even with the volume knob dimed. This was the case with both channels. I took a peek at the tubes and noticed that the heater in the phase inverter (a 12AT7) was not aglow, while the other tubes were lit-up. I shut down and then removed and tested all the tubes in my Jackson tube tester, and all tested good. Odd.

This weekend, I finally got around to removing the chassis. I discharged the filter caps and took a peek at the guts and particularly the wiring around the phase inverter's socket. Everything appeared to be okay. Using a multimeter, I found that the heater pins were receiving the correct amount of voltage. I then placed a single 12AT7 tube into the socket, hooked the amp up to a Variac and, still having my multimeter connected, found that the tube's heaters did indeed light-up and that the voltage was correct. I then replaced all the tubes, hooked-up to the speaker and fired her up, but this same phase inverter tube failed to glow! I then removed the two 6V6 power tubes while keeping all of the other tubes intact, and voila . . the phase inverter lit-up! Any ideas what could cause this? Perhaps a bad socket? I thought I'd get some opinions before proceeding further.


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Sun Mar 27, 2011 9:29 pm
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Check the soldering of the power tube socket heater pins. You could get 6.3 VAC onto the PI, but a bad solder or power tube socket maybe robbing some of the current.

Also, check to be sure that the solder on that PI is good too. Remember both 4 & 5 pin of the 12AT7 should be tied together and go to one line. And the 9 pin the the other. All the lines are in parallel. So, it's possible to get inadequate current to one tube, yet perfectly ok current to tubes downstream.

Good luck with that!


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Sun Mar 27, 2011 9:31 pm
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Hi tricone,

It may be a bad PI tube or an output tube/tubes, or the socket/sockets, or even bad solder joints. A tube tester is limited and won't always detect a bad tube. Sounds like you've inspected the solder joints, and they seem OK at the socket and at the other end of the wires for the filament supply? Easy enough to try a new PI tube and/or a set of output tubes. Typically, a 12AT7 will not light up nearly as bright as a 12AX7, sometimes unnoticeable next to other tubes. You might also try re-tensioning the tube sockets if the new tubes don't fix it. Here are instructions on how to re-tension the sockets (link below). Make sure that the amp is off and unplugged and caps discharged before re-tensioning tube sockets. My first thought would be the output tubes, then PI tube, then sockets. :)

http://billmaudio.com/wp/?page_id=171

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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Sun Mar 27, 2011 10:02 pm
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BMW2002Ti wrote:
Check the soldering of the power tube socket heater pins. You could get 6.3 VAC onto the PI, but a bad solder or power tube socket maybe robbing some of the current.

Also, check to be sure that the solder on that PI is good too. Remember both 4 & 5 pin of the 12AT7 should be tied together and go to one line. And the 9 pin the the other. All the lines are in parallel. So, it's possible to get inadequate current to one tube, yet perfectly ok current to tubes downstream.

Good luck with that!


I first tested the resistance to all the heater wires going to and from the particular socket, along with the wires from the the other pins. I did note that pins 4 and 5 are tied together. I also examined the wires and solder joints coming from the power tube, and they appeared to be okay. I took a multimeter and tested all the wires coming to and from the PI, and all appeared to be okay. I was next going to try and resolder the heater wires/terminals, but thought I'd pose this question first. It just was strange how, once the power tubes were removed, the phase inverter lit-up, but when the two 6V6s were present . . darkness. Oh, and I did use Deoxit to clean the pin sockets.


shimmilou: I neglected to mention that I did use a known-good NOS JAN 12AT7 that functions fine in another amp. I have a nice little Emery Sound MicroSpotlight that also doubles as a "live tube tester" (as opposed to my Jackson 648S) in that it accepts just about any preamp tubes from 12AX7s to CV4003s and multiple power tubes, including 6V6/6K6/6G6/EL33 and EL84s! After reading your post, I took the 6V6s from the BFDR and tested both in my Emery Sound amp and both functioned fine, as did the 12AT7. I'll try the re-tensioning of the power tube sockets tomorrow. Thanks for that link!


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Sun Mar 27, 2011 10:33 pm
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Yeah, I've had problems in the twisted pair of heater lines in older amps. The wire sometimes gets a bit stiff and can break. Esp at the solder points of each tube socket. I've actually had to re-wire some older amps. You can tell by tapping the lines when the amp is on.

Good luck!


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Sun Mar 27, 2011 11:08 pm
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You might check the .1mfd coupling caps going into the PI for DC leakage.

Arjay

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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Tue Mar 29, 2011 8:46 am
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I believe I narrowed it down to a bad socket. Reflowed solder on all the heater wires to and from the PI socket, along with the tabs at the adjacent power tube socket. Retensioned and cleaned the power tube sockets. Fired the amp back up, but the PI's heaters failed to glow. Wiggled the tube a bit and got some juice. If I aligned the tube 'just so', the tube remained lit. Played a guitar through the amp just to be sure it was okay. Powered down, removed the PI tube, replaced it and fired it up again. In order to get the PI to glow, I again had to play around with its position in the socket. I have a small tool that allows me to retension the smaller 9-pin sockets, so I attempted to do so (after discharging the caps). However, I still have to reposition the PI tube by wiggling to get juice. I'll order a new socket and go from there. Thanks for everyone's suggestions!


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Tue Mar 29, 2011 2:14 pm
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Tube sockets sometimes fail due to heat and age -- I've diagnosed a few over the years. Try to find an NOS type replacement to keep the amp looking vintage and be sure to "recycle" your tube shield.

Arjay

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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Tue Mar 29, 2011 2:21 pm
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Retroverbial wrote:
Tube sockets sometimes fail due to heat and age -- I've diagnosed a few over the years. Try to find an NOS type replacement to keep the amp looking vintage and be sure to "recycle" your tube shield.

Arjay


Arjay . . any idea where one can find an NOS replacement? I ordered one from Antique Electronic Supply, but might also looks for one that is more "vintage." Ebay?


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Tue Mar 29, 2011 2:51 pm
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Yeah, Ebay is a good source for NOS parts.

Beware a socket that's been "harvested" from a vintage piece of gear -- like as not, it may have been a problem-part that somebody tossed from a chassis and is now brooming off to the unsuspecting.

HTH

Arjay

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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Tue Mar 29, 2011 4:38 pm
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I've gotten a bunch of real mil spec Amphenol from Clark Labs over the years, Mostly octal sockets. They've all come in sealed military issued packets (see the old Army triangular logo on each package). They are the real thing. Best sockets made in my opinion. YOu can email him. He used to advertise 9-pin mini mil spec sockets on EBay.

http://cgi.ebay.com/NOS-Amphenol-8-Pin- ... 2eb154755c

For 9-pin Russian ceramic are pretty good. Most are are mil spec leftovers from the Cold War. Be sure they have holes in the socket tangs to route and secure wires prior to soldering. A lot of aftermarket 9-pin sockets these days lack this, because they are designed to fit into circuit boards.

http://cgi.ebay.com/9-pin-TUBE-SOCKETS- ... 2eb3c0e163


MEASURE SOCKET HOLE DIAMETER & DISTANCE FROM SCREW MOUNTS. You do not want to be mucking around trying to squeeze a not-quite-right sized socket into your unit, if possible.

Good luck with you amp!


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Wed Mar 30, 2011 9:47 am
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tricone wrote:
Retroverbial wrote:
Tube sockets sometimes fail due to heat and age -- I've diagnosed a few over the years. Try to find an NOS type replacement to keep the amp looking vintage and be sure to "recycle" your tube shield.

Arjay


Arjay . . any idea where one can find an NOS replacement? I ordered one from Antique Electronic Supply, but might also looks for one that is more "vintage." Ebay?


Check out Angelas Instruments. Good stuff, cool people, and decent prices on many of their items. In my experience anyway. have the dimensions of the socket you need and make a match. The yhave old looking stuff made out of the brown plastic composite like material.
http://angela.com/


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Wed Mar 30, 2011 10:08 am
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mxvin wrote:

Check out Angelas Instruments. Good stuff, cool people, and decent prices on many of their items. In my experience anyway. have the dimensions of the socket you need and make a match. The yhave old looking stuff made out of the brown plastic composite like material.
http://angela.com/


Thanks for the tip. I've heard of Angela, but had forgotten about them. I'll check them out. Having said that, I'm looking to match the tube sockets in my BFDR, which have the black bases.


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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Thu Mar 31, 2011 1:05 am
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I once had an issue with fuses popping and tube overheating. And it ended up being BOTH a bad rectifier wiring, AND one power socket. PLUS, stiff hinky heater wiring to the said power tube socket, that prolly kept leading to broken solder. This was after I replaced the PT, which was fried in original amp. The fired PT could have been due to all this bad brittle wiring.

I put in Mercury PT. Mil spec Amphenol sockets and retwisted the wiring between rectifier sockets and between the two power tubes. Changed out screen resistors (you can see them peeking through the hole in the power tube socket. The one thing I LOVE about Amphenol (besides they last forever), is their tangs are pre-tinned. Makes soldering twisted pairs and resistors a breeze.

Good luck with your project!

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Post subject: Re: Help: Puzzling Issue with a '66 BFDR
Posted: Thu Mar 31, 2011 7:43 am
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After looking over various posts on the internet, I've been 'hearing' more and more issues with bad tube sockets. It turns out with my BFDR, I used a home-concoted tool to retension the smaller 9-pin pin sockets, and that seemed to do the trick. Now, knock on wood, the amp fires-up as its supposed to. I played through it off-and-on for a couple of hours yesterday, with no issues. :D

Just in case, I did order a replacement tube socket, but I'll probably hold-off installing it for now.


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