6BQ5/EL84

[jaymanaa]

A lot of you guys that are building maggies and other console amps, can do a simple e-wire on the 6BQ5 socket and run the 6GK6. They are a little cheaper still and seem to have a little better woofer control down low (just a little). Tons of them were made for Setchell Carlson TVs and those are all Amperex. A S/C 6GK6 is much cheaper than an Amerex 6BQ5. You can also add a 10 volt fil TX for super cheap, esp,for the ST35 and run 10BQ5s while taking a bit of load off the already way stressed ST35 PT.

 

[reaper996]

Have you thought about the 6P14P russian tubes? I purchased 4 quartet sets from gobble75 on Fleabay. I had only one bad tube out of the lot. I am using them in my 9303 and Tubelab SPP. Joe does a really good job matching them. I am not affiliated with the seller, just passing along my experience.

 

[Shadowdog]

One thing is you can run high voltage on the tough tubes even over 400V to 430V on the plates as long as you run
330V or less on the screens as George Anderson of Tubelab.com found out with his JJ's about 5 years ago.

 

[whoaru99]

With a cathode bias p-p amp can you get adequate matching by just trying tubes until you find pairs that draw about the same current?

I understand there's likely a lot more to a good match than that, but I don't know anyone relatively local that has an actual tube tester.

 

[gadget73]

You can, sure. Just need a way to monitor each tube individually to match them up. The idea is to get equal current on both sides of the output transformer. If the idle current runs the same, that'll get you most of the way there even if it swings some with signal input. Tube testers are usually fairly crap for matching honestly unless its one specifically designed to match by power output and idle current.

 

[whoaru99]

I'll have to wait until the amp shows up to have a better idea of space. But, could the 130 ohm cathode resistor be replaced with a 120 ohm, then "Y" from that to each tube with its own 10 ohm?

Or, would it be better to replace the single 130 with two individual of (half or twice??) the value?

 

[peterh]

Keep the 130 ohm and replace the tubes with a matched pair ( matched at 300V )

 

[whoaru99]

Maybe down the road, but at present I have a plan that does not include buying matched tubes.

 

[Harlon]

I picked up a matched set of TAD EL84STR's a bit back and am lovin' them. Those are a heavy duty version, similar in construction to the 7189 industrial tubes. They'll run fine at "stock" power levels, but you can push more watts if your amp has the iron for the job. That said, if you run them at stock settings, you'll end up with a bit more headroom - never a bad thing. Heavy glass which makes them slightly larger than a standard tube, so keep that in mind if your tubes are piled in tight.

Here's the spec sheet.

https://www.tubesandmore.com/sites/default/files/associated_files/t-el84-tad.pdf

I also am shopping for a set EL84s. I think I've got it narrowed to some Sovtek EL84Ms from Mcshane or a set of the TAD STRs. I've read a ton of good things about the TADs on the guitar forums. Anyone else had good results using them with hifi?

 

[thorpej]

I also am shopping for a set EL84s. I think I've got it narrowed to some Sovtek EL84Ms from Mcshane or a set of the TAD STRs. I've read a ton of good things about the TADs on the guitar forums. Anyone else had good results using them with hifi?

I'll just put in another +1 on the Sovtek EL84M. They sound great in my AA-151.

 

[gadget73]

I'll have to wait until the amp shows up to have a better idea of space. But, could the 130 ohm cathode resistor be replaced with a 120 ohm, then "Y" from that to each tube with its own 10 ohm?

that'll do it. You can modify it to have a high wattage pot in there to balance them out too. The old Williamson amps did it that way, but they did current monitoring by directly inserting the ammeter in the cathode. I'd probably do fixed resistors and measure voltage drop though, just because I'm not a big fan of breaking current flow to jam a meter in when I don't absolutely have to.

 

[jaymanaa]

I'll have to wait until the amp shows up to have a better idea of space. But, could the 130 ohm cathode resistor be replaced with a 120 ohm, then "Y" from that to each tube with its own 10 ohm?

Or, would it be better to replace the single 130 with two individual of (half or twice??) the value?

You never want to run a single cathode R on a stereo PP amp. The only reason they did that was to keep costs down. You at least want a cathode R on each pair of tubes to have a chance at a soundstage. What I do with console amps is run a cathode R on each output tube, bypassed by about 470uf of lytic. Some people here will tell you that you have to have bi-polar caps between the tubes for reference, but I've got plenty running just as simple as I first stated. This also lowers the power value of the cap, giving you more choices. Four tubes, four resistors, then run a meter probe up top so you can monitor current draw (using DC voltage) and match tubes in circuit where it matters. It's so easy to make thee amps sound good, and IMO a 12AT7 front end, and a modified output stage like I described will do more for amps like the 9302 than buying a cheap pair of output TXs. The stock units can be made to go down around 40 before saturation. I'd be curious to know how many people here are running under 40 HZ without a sub on any budget stereo. I'd also like to know how many music programs we listen to that make the under 40 demand on our system. My Dynaco 70 will saturate at 25hz at 50 watts per channel, both channels operating, but very few things I listen to require such extremes. Techno's dead guys.

 

[jaymanaa]

I'll just put in another +1 on the Sovtek EL84M. They sound great in my AA-151.

Stock OPTs?

 

[whoaru99]

I don't have the amp yet, but according to the schematic it does have a cathode resistor for each pair of tubes. Splitting out separate or adding some sort of balance shouldn't be a problem.

And, the amp does have a 12AT7 front end as stock/OEM. I'm hoping it ends up being a sweet little amp.

 

[GordonW]

Sovtek EL84M will run in 7189 conditions as well, so they just breeze along at 6BQ5 specs. Sound good too.

This. I've used LOTS of these. They just don't fail. And, yes, they do sound good. I ran them in my SC ASR333 for many years.

Regards,
Gordon.

 

[jaymanaa]

I don't have the amp yet, but according to the schematic it does have a cathode resistor for each pair of tubes. Splitting out separate or adding some sort of balance shouldn't be a problem.

And, the amp does have a 12AT7 front end as stock/OEM. I'm hoping it ends up being a sweet little amp.

This. I've used LOTS of these. They just don't fail. And, yes, they do sound good. I ran them in my SC ASR333 for many years.

Regards,
Gordon.

I've turnt some cherry red,but ain't never blowed one up. What convinced me, is Dan (Celt pronouced Kekt) uses these and he repairs geetar amps that absolutely can't fail in the middle of dueling Banjos. If he trusts them,I trust them, and then the SQ was fine as fog hair too, so winner winner chicken dinner.


Don't get me started on the AA151, trust me. If youhave a 70, sell that 151 and put the money in the 70, the 151 is an abortion. Was that attitude, if so I apologize to any deaf folk who own AA151s. Did you guys ever see my 151, it weighs in at 72 pounds?

 

[whoaru99]

The mystery amp/application, the underlying point of this thread, is a Victor Audiola (JVC?) MST-30.

 

[Pio1980]

I've turnt some cherry red,but ain't never blowed one up. What convinced me, is Dan (Celt pronouced Kekt) uses these and he repairs geetar amps that absolutely can't fail in the middle of dueling Banjos. If he trusts them,I trust them, and then the SQ was fine as fog hair too, so winner winner chicken dinner.


Don't get me started on the AA151, trust me. If youhave a 70, sell that 151 and put the money in the 70, the 151 is an abortion. Was that attitude, if so I apologize to any deaf folk who own AA151s. Did you guys ever see my 151, it weighs in at 72 pounds?

The 151 has a great power amp coupled to a perplexing preamp section. The tone section stinks on ice, and the phono and line inputs have an inverted acoustic polar relationship.

 

[thorpej]

Stock OPTs?

Yes.

 

[thorpej]

The 151 has a great power amp coupled to a perplexing preamp section. The tone section stinks on ice, and the phono and line inputs have an inverted acoustic polar relationship.

Yah, I'm aware of the AA-151's limitations. I only use a single line-level source with it, so I limit my exposure to some of its problems. One of these days I may get ambitious enough to spend some time on the front-end, but for now it's perfectly fine for how I use it.