101B

[101B /^/]

Greetings - I’m a long time xtc owner but this is my first post on Rig Talk.

I have a few questions that are a bit out of my wheelhouse so I was happy to find a Bogner-specific forum that seems to have a good knowledge base. Bogner Amplification's been a little difficult to contact these days..

I acquired the amp second-hand in 2004 and if I recall correctly it’s a 2003 build. S/N = K /^/ which I think makes it xtc#1121?

My main question for the experts regards plate voltage and if my voltage & bias readings indicate any sort of potential issue.

Context: I had a quad of new production Mullards in the power section that I’d used for several years but recently one of the tubes red-plated while running the amp in Class A. Old notes indicate plate voltage ranged from 535-540 and I had the tubes biased at approx 32ma (I’m fortunate to have a Weber Bias-Rite).

After losing the Mullard I installed a quad of Svet winged-c’s and I’m seeing plate voltages running between 550-555 with the tubes biased at approx 36ma. Amp sounds great (as usual), but, I’ve been avoiding using it in Class A because it seems like my plate voltages are running higher than they once did and I’m concerned something might be throwing warning signs. I seem to recall Bogner always recommended around 32ma..

Thanks in advance and here’s a few recent snapshots of my baby!

 

[Rocker68]

Greetings ,
You will probably get some useful information here . Regarding your issue , Class A aside , running the EL 34 tubes at 32 ma via 550 VDC @ plate ( pin 3 ) , yields a stonking 80@% !!!!!
Not the end of the world but , crank the bias down to a conservative 26 ma and give the tubes a healthy chance .
( like 60 % )
Start with the plate voltage then adjust the ma . Recheck with each adjustment as it could lower the VDC further .
Zero all volume and gain knobs before taking readings .
While observing the ma readout , zero all presence knobs to see if it changes the readout value . May or may not .

 

[skoora]

Greetings ,
You will probably get some useful information here . Regarding your issue , Class A aside , running the EL 34 tubes at 32 ma via 550 VDC @ plate ( pin 3 ) , yields a stonking 80@% !!!!!
Not the end of the world but , crank the bias down to a conservative 26 ma and give the tubes a healthy chance .
( like 60 % )
Start with the plate voltage then adjust the ma . Recheck with each adjustment as it could lower the VDC further .
Zero all volume and gain knobs before taking readings .
While observing the ma readout , zero all presence knobs to see if it changes the readout value . May or may not .

Yeah, my first thought was about getting the bias into the 20’s at that plate voltage. Also does the same position redplate between the different tube sets?
With the Mullard’s does the red plating follow the tube, no matter where you put it?

 

[101B /^/]

Thank you for your posts, I appreciate the caution and the tips..seems I’ve come to the right place.

First, to clarify - I’ve been using the amp with a different set of tubes rather than those cited in my initial post (ie: quad biased at 34-36ma). But, my concern remains due the plate voltage which seems to have mysteriously risen over the yrs??? What’s that all about?

The tubes currently in the amp (also =c=) are biased (by pair) at 26.6 in V7/V9 & 32.5 at V8/V10. I’ve been using the amp on 1/2 power, but no Class A.

Rocker68: After reading your post I fired it up, zeroed all vol/gain and also the presence knobs while taking measurements - no changes to ma's throughout the entire sweep of the presence knobs. Everything appears steady.

skoora: red-plating follows the tube, so sadly the quad now has a bum tube.

Probably rookie questions but, how does one lower plate voltage? Is there a simple adjustment that doesn’t involve a soldering iron or lethal shocks?

BTW, the new prod Mullards are the goods in my amp and will ultimately replace them. Can the xtc run on two tubes?

 

[skoora]

Thank you for your posts, I appreciate the caution and the tips..seems I’ve come to the right place.

First, to clarify - I’ve been using the amp with a different set of tubes rather than those cited in my initial post (ie: quad biased at 34-36ma). But, my concern remains due the plate voltage which seems to have mysteriously risen over the yrs??? What’s that all about?

The tubes currently in the amp (also =c=) are biased (by pair) at 26.6 in V7/V9 & 32.5 at V8/V10. I’ve been using the amp on 1/2 power, but no Class A.

Rocker68: After reading your post I fired it up, zeroed all vol/gain and also the presence knobs while taking measurements - no changes to ma's throughout the entire sweep of the presence knobs. Everything appears steady.

skoora: red-plating follows the tube, so sadly the quad now has a bum tube.

Probably rookie questions but, how does one lower plate voltage? Is there a simple adjustment that doesn’t involve a soldering iron or lethal shocks?

BTW, the new prod Mullards are the goods in my amp and will ultimately replace them. Can the xtc run on two tubes?

I believe when in half power it is running on two tubes. Old/New is pentode vs. Triode. Even thought the Bogner website is crap I believe they are very responsive at their email address. I think it’s..

Info@bogneramplification.com

Try the Bogner manufacturer sub forum on here as well.

 

[101B /^/]

I believe when in half power it is running on two tubes. Old/New is pentode vs. Triode. Even thought the Bogner website is crap I believe they are very responsive at their email address. I think it’s..

Info@bogneramplification.com

Try the Bogner manufacturer sub forum on here as well.

Indeed 1/2 power = 2 tubes, but can you literally pull two of them out? I’ll email Bogner and ask - thanks for their address (I typically call).

I usually have the amp on Old + 1/2 power, but do use all settings at any given time depending on what I want to hear.

 

[Rocker68]

Some power tubes will draw more current . I've run across Hot EL 34 's testing @ 70 ma and as low as 20 . This is the high , med , low RATING
the vendor uses . The high can alter the VDC to
undesirable levels to some degree . When you buy a new matched quad , you should indicate what your expectations are . Diplomatically request
" matched within 3 - 5 ma . The final bias will be 20 - 30 ma ."
In so many words .
Contact J O R G at BOGNER for specific answers . He will not disappoint . However , he is swamped , so allow a minimum of three business days for a response . If crickets , substitute the
word " Info " with " Sales " .

What does the Red plating tube display on the
Bias Rite ? It might not be landfill material .

 

[101B /^/]

Some power tubes will draw more current . I've run across Hot EL 34 's testing @ 70 ma and as low as 20 . This is the high , med , low RATING
the vendor uses . The high can alter the VDC to
undesirable levels to some degree . When you buy a new matched quad , you should indicate what your expectations are . Diplomatically request
" matched within 3 - 5 ma . The final bias will be 20 - 30 ma ."
In so many words .
Contact J O R G at BOGNER for specific answers . He will not disappoint . However , he is swamped , so allow a minimum of three business days for a response . If crickets , substitute the
word " Info " with " Sales " .

What does the Red plating tube display on the
Bias Rite ? It might not be landfill material .

When buying tubes in the past I’ve always told the vendor my plate voltage and request tubes that will bias on the warmer side (ie: bias around 28-32). I’ve always used ’32' as the targeted max I wanted to see. Although that’s worked in the past, not so much now. I do recall Mesa had the low, med & high ratings on their boxes.

Quad of Mullards were new when I installed them shortly after they hit the market. The red-plated tube (when new, and after burn in) had a plate voltage of 539 and was biased at 30.8. After red-plating - the plate voltage measured 554 and 35ma..thing is the bias reading was rising and was running away, so I shut it down. Repeated the same step in an adjacent socket (other “pair” in the amp), and got the same result with that particular tube. I just assumed that tube was toast.

 

[skoora]

When buying tubes in the past I’ve always told the vendor my plate voltage and request tubes that will bias on the warmer side (ie: bias around 28-32). I’ve always used ’32' as the targeted max I wanted to see. Although that’s worked in the past, not so much now. I do recall Mesa had the low, med & high ratings on their boxes.

Quad of Mullards were new when I installed them shortly after they hit the market. The red-plated tube (when new, and after burn in) had a plate voltage of 539 and was biased at 30.8. After red-plating - the plate voltage measured 554 and 35ma..thing is the bias reading was rising and was running away, so I shut it down. Repeated the same step in an adjacent socket (other “pair” in the amp), and got the same result with that particular tube. I just assumed that tube was toast.

If it followed the tube, that may just be the issue and the amp is fine. Does the amp have a bias adjust inside? If so you can get any decent matched quad and adjust to be in the right range. If the Svet’s aren’t doing it, pop it in Class A and see what happens. But I would see about getting the bias lower on them, closer to 30 or high 20’s. Hopefully Bogner will get back to you and clarify.

 

[101B /^/]

If it followed the tube, that may just be the issue and the amp is fine. Does the amp have a bias adjust inside? If so you can get any decent matched quad and adjust to be in the right range. If the Svet’s aren’t doing it, pop it in Class A and see what happens. But I would see about getting the bias lower on them, closer to 30 or high 20’s. Hopefully Bogner will get back to you and clarify.

Definitely hoping the amp’s okay and I’m composing an email for Jorg. Also plan to do some more trouble shooting. The amp has a single trim pot accessible from the chassis’ topside.

Last night, after reading yesterday's posts and at your guidance, I fired-up and adjusted bias down to 29 on the hot pair of tubes presently in the amp at V7/v9 & the cold pair at V8/V10 are biased at 24. Pushed the amp a bit and let all settle. This morning, bias is steady and I plan to test the tubes in Class A to see where the bias is at using the current setting in A/B ahead of my email to Bogner.

 

[itsme]

Keep in mind Bogner’s are supposed to run at 117 volts. If your wall voltage is 120 or greater, that increases internal voltages and adds stress. I bias my 101B at 32 mv and run my wall voltage between 115-117 using a brown box. I use regular JJ EL34’s and have no issues

 

[101B /^/]

Keep in mind Bogner’s are supposed to run at 117 volts. If your wall voltage is 120 or greater, that increases internal voltages and adds stress. I bias my 101B at 32 mv and run my wall voltage between 115-117 using a brown box. I use regular JJ EL34’s and have no issues

Just received notification from Jorg and he’s giving my amp a clean bill of health, so I’m happy. I tested my bias on Class A and saw voltage drop slightly and the tubes bias jumped to 75ma, so I shut down to be cautious. Pretty warm, but Jorg says that's the tube doing what it’s supposed to do and he attributes the voltage spike I’m seeing to my wall voltage. I do plug straight into the wall through a surge protector and generally get a consistent 121-122 AC delivered by the power co. Although I'm very familiar with industrial buck/boost transformers and how cnc equipment can be sensitive to power fluctuations, I confess, I don’t know what a brown box is..do tell. It clearly regulates power and I’d love a cheap way to bring my voltage down..then again, my amp is beast and I’d hate to give up some of that fire. I think Angus Young lets tubes cook for hrs before a show..lol. I can’t afford tubes like Angus can.

 

[skoora]

Just received notification from Jorg and he’s giving my amp a clean bill of health, so I’m happy. I tested my bias on Class A and saw voltage drop slightly and the tubes bias jumped to 75ma, so I shut down to be cautious. Pretty warm, but Jorg says that's the tube doing what it’s supposed to do and he attributes the voltage spike I’m seeing to my wall voltage. I do plug straight into the wall through a surge protector and generally get a consistent 121-122 AC delivered by the power co. Although I'm very familiar with industrial buck/boost transformers and how cnc equipment can be sensitive to power fluctuations, I confess, I don’t know what a brown box is..do tell. It clearly regulates power and I’d love a cheap way to bring my voltage down..then again, my amp is beast and I’d hate to give up some of that fire. I think Angus Young lets tubes cook for hrs before a show..lol. I can’t afford tubes like Angus can.

You can get variacs off Amazon that are less than $100. These allow you to set the output voltage with a dial. I bought one. A while ago but haven’t set it up yet. They won’t maintain constant voltage like a voltage regulator would (they’ll mirror the ups and downs of the wall voltage) but you can use it to knock a bit off and get it to 117 or lower if you want to. But if the a,p is working fine and it was just a tube, I wouldn’t sweat it too much. What did Jorg recommend for a bias setting in A/B?

 

[101B /^/]

You can get variacs off Amazon that are less than $100. These allow you to set the output voltage with a dial. I bought one. A while ago but haven’t set it up yet. They won’t maintain constant voltage like a voltage regulator would (they’ll mirror the ups and downs of the wall voltage) but you can use it to knock a bit off and get it to 117 or lower if you want to. But if the a,p is working fine and it was just a tube, I wouldn’t sweat it too much. What did Jorg recommend for a bias setting in A/B?

Ah, a variac - I understand now, that is an inexpensive workaround..thank you for that. Jorg explained the only thing that will cause a rise in voltage is the input power, and not a failing component. He said my amps running on the warm side but to just use the amp and keep it biased between 28-32 but perhaps keep it on the cooler side considering my input voltage. I don’t recall for certain my wall voltage was where it’s been the last several yrs and it’s not inconceivable we were in the 118-120 vs steady 122 today. That explains the rise in plate voltage. An abundance of caution on my end, thankfully.

I really appreciate all that chimed-in while I worked through my concern - the xtc is such a wonderful amp, I’d hate for something to go silly with it.