Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: RPMac on April 07, 2014, 07:18:09 AM
-
Is there any problem with running the BeePre full time with 6A3's?
-
This shouldn't be a problem.
-PB
-
I have been using 6A3s since Jan. I only use it maybe 2 hours a wwek but they have been fine for me.
-
Why would a 300B work in my ParaBee, but not in the BeePre?
These are unknown Chinese-made solded by Upscale Audio that I bought used(actually one worked, the other didn't)
Could it be a weak tube?
-
If the filament is sufficiently out of tolerance, then perhaps that could cause an issue.
Taking some voltage measurements of the tube that doesn't work operating in the BeePre would tell us for sure.
-
300B's
tube 1...Fil--4.23vdc; Plate--142vdc
tube 2...Fil--4.25vdc; Plate--144vdc
tube 1 was playing, then faded out as I was taking measurements.
Put the 300B's back in ParaBee's and I'm listening to them now.
6A3's in BeePre
tube 1...Fil--6.13vdc; Plate--101.2vdc
tube 2...Fil--5.90vdc; Plate--98.8vdc
-
Yeah those cathodes are exhausted.
-
300B's
tube 1...Fil--4.23vdc; Plate--142vdc
tube 2...Fil--4.25vdc; Plate--144vdc
Those 300B's aren't really drawing any plate current. What is your "POS OUT" voltage from each regulator board?
This is about what I'd expect from some well worn 300B's. They'll still work in a cathode bias power amp (kinda), but not in something as tightly regulated as the BeePre.
-
I'm assuming you mean the high voltage reg (ter.6--144.8vdc & ter.11--145.9vdc)
The Pos Out on the PSU board 10.07vdc & 10.00vdc
Measured with 6A3's in.
As for the 300B's, I guess that is what you get with a cheap "deal" on eBay.
In the BeePre, would a plate voltage much above ~100vdc or +110vdc indicate a tube that is expiring?
-
...
In the BeePre, would a plate voltage much above ~100vdc or +110vdc indicate a tube that is expiring?
I'd say "fading". It should still work until the plate voltage is around 135v - that leaves 10v compliance to the regulated 145v, so you still have 5v peak output available with a 5v margin for the C4S to function properly. So at maybe 130v I'd say "expiring".
-
PJ, thanks for the explanation. I don't understand how a constant current source works, but thought Ohm's Law had to apply in some way.
-
PJ, thanks for the explanation. I don't understand how a constant current source works, but thought Ohm's Law had to apply in some way.
Yeah, a current source replaces a resistor (fixed, resistive impedance at the frequencies we care about), with an impedance that is much higher.
Since you're cool with Ohm's law, we'll look at the voltage amp stage in the defunct Foreplay III as an example:
The stock circuit drops about 3.3mA across a 22.1K resistor from a 150V power supply, so 75V appears on the plate of the first stage.
When we install a C4S in this circuit, the 22.1K resistor is removed and replaced with a current source set to about 3.3mA. Consequently, the same plate voltage appears, but the load impedance that that gain stage sees is now several million Ohms (instead of 22,100 Ohms).
It isn't necessary to understand the workings of the current source, but rather that it allows us to circumvent the restrictions of Ohm's Law a bit. If we wanted that same gain stage with a 1M plate load resistor, 75V on the plate, and 3.3mA of current, we would need a 3,200V power supply and a 1M 30W resistor. When you go through the analysis, you need hundreds of dollars worth of parts to build a 3.2kV power supply, then you need those resistors too (they are about $100 each), then the pin spacing on the 9 pin socket would cause a lot of arc over before the tube drew current, etc.
-
I've heard good things about the 6a3 tube option in the BeePre forum, and I am leaning in that direction. I'm seeing NOS Philco, RCA, Sylvania, etc. pairs on eBay. Is there any consensus as to which of these NOS brands/versions are preferable? Thanks.........
-
Have you tried it with a 300B yet?
-
No- I've just started the build. Since some of these tubes take a long time in shipment, I want to reach a decision. My logic on the 6a3 after research here is that: a)there are claims that they are less microphonic b) you can get vintage NOS American made tubes for around $150 matched pair which (in theory) means improved sound. I guess the 6a3 filaments have higher resistance, so filament voltage is pretty acceptable at around 6.1VDC. My guess is that the preamp with 6a3's may have less overall gain, but nobody has complained. If I go with 300B's, NOS not available at my price range. Looking at buying stock EH 300B's from you (if available separately), TJ Mesh, Psvane TII (currently in my Paramount 1.1's- $400), or whatever else my research digs up. I'm looking for feedback because I'm hoping to "buy once".
That said, I'm all ears on whatever advice you might have :). Excited about hearing combination of BeePre>Paramount 1.1>soon to be purchased Fostex BK-16 folded horn kit with Fostex FE168 Sigma full range drivers. Thanks, Kip.............
-
Just to be clear, the BeePre was designed and "tuned" around the EH 300B. It is a fortuitous accident that a 6A3 will also work.
-
As Paul said, it is just fortuitous that the 6A3 will work in the BeePre. I would concentrate on the 300B & think of the 6A3 as a different 'flavour' you can try at some point.
It's a while since I had 6A3's in the BeePre, but I don't recall any noticeable difference in gain & no 'improvement' in sound, just a slightly different presentation.
Buying NOS tubes on Ebay is a crapshoot at the best of times. There are plenty of NOS tube dealers who know what they're doing & usually cost less than what you'll pay on Ebay. Just checked a few sites and NOS 6A3 go for $25-40 each.
-
Chris65:
What are you running in your Beepre? Any favorites?
I'm always interested to find better tube sources- if you have a moment, I'd appreciate it if you could direct me to some of the quality tube vendors you mentioned.
Of course, there's always this option:
http://www.ebay.com/itm/MP-of-Western-Electric-300B-Tube-Double-Square-Getter-NOS-NIB-Date-code-6539-/301635864396?hash=item463ae6074c:g:IfIAAOSw0vBUcAM5
WOW!
Thanks for your time, Kip..........
-
I have been using Sylvania NOS 6A3s and have been very happy with them. They are not as tall as 300Bs and fit better in my rack. I do have a pair of JJs and EHs for it, but they barely touch the bottom of the shelf above the amp.
-
I have been using Sylvania NOS 6A3s and have been very happy with them. They are not as tall as 300Bs and fit better in my rack. I do have a pair of JJs and EHs for it, but they barely touch the bottom of the shelf above the amp.
Other than the rack issue, do you have a favorite- or all pretty close?
-
I use 6A3's as my "everyday" tubes because of $$$$. ( Raytheons right now ) l've had good luck from eBay.
As Doc said, the BeePre was developed and voiced with EH 300B's...probably the best place to start.
I agree with Chris, it's a matter of "flavor". Depends on speakers and room effects, then what amp, and then what you like.
I believe the design and using a DHT makes it a great preamp. Thanks PJ!!
Would be interesting if PJ could come up with a mod to use 10Y family of tubes.
-
Would be interesting if PJ could come up with a mod to use 10Y family of tubes.
The 10Y needs a lot more plate voltage than is available in the BeePre to run in class A1, which makes it not such a suitable choice.
I was commissioned not that long ago to build a preamp using the 12A/112A. The microphony was very difficult to deal with, and required a significant redesign to the circuit that ultimately undermined the compatibility of the preamp significantly.
In the simplest terms, the 12A can only run 10% of the current and will have 10x the output impedance with more microphony...
-
Chris65:What are you running in your Beepre? Any favorites?
I'm always interested to find better tube sources- if you have a moment, I'd appreciate it if you could direct me to some of the quality tube vendors you mentioned.
No particular favorite, usually running 300B, sometimes 6A3. I enjoy both. And a 6B4G with adapter works too.
If you search 'NOS tube suppliers' you'll find plenty of dealers. Also try vintage radio parts or similar.
I've had, or heard of good experiences from these but there are many others (guess it's ok to post links? :) )
https://vacuumtubesinc.com (https://vacuumtubesinc.com)
http://www.findatube.com (http://www.findatube.com)
http://www.vacuumtubes.net (http://www.vacuumtubes.net)
-
Other than the rack issue, do you have a favorite- or all pretty close?
Pretty close, 300b is slightly more detailed.
-
Chris65:
I also found The Tube Center in Orlando.
http://www.thetubecenter.com/
I think the reason I might not have paid much attention when I stumbled across a site like these is that there is not a lot of detail or specific info like photos, possible matching, written description, etc. Guess that's because you're getting a better price and they don't have time for the advertising and presentation. Also, I believe they do not sort or match as much- if at all. Just missed getting some 6A3's for $35 each at The Tube Center.
-
Chris65:
I also found The Tube Center in Orlando.
I don't get it. Do you have to call to see what is in stock or what brands/types of each tube are available? Seems weird that they have 1 price listed for each tube type. Some of which seem very very low.
-
scotth:
I called the guy at the Tube Center, and he was real approachable. The website says they have 3.5 million tubes under one roof. He described the tubes, and said someone bought all six. Asked me to email him with info on tubes I was looking for, and he would call me when some more came in. Does not offer matching, but he said he felt that if the tubes were in a lot, might be close enough anyway.
I'm starting to wonder how important matching is in this application- does C4S reduce the importance of matching? Is it important at all? I get the impression that many people may be using unmatched tubes in their BottleHead equipment, but don't really know.
-
I also found The Tube Center in Orlando.
I think the reason I might not have paid much attention when I stumbled across a site like these is that there is not a lot of detail or specific info like photos, possible matching, written description, etc.
Yes, as I said there are many tube suppliers. If you're concerned about details like this, you can always ask.
It would be a massive task to sort this kind detail if any sizeable amount of stock was held.
For info:
Matching between channels in a single ended amp is not particularly important. -PB
-
No particular favorite, usually running 300B, sometimes 6A3. I enjoy both. And a 6B4G with adapter works too.
If you search 'NOS tube suppliers' you'll find plenty of dealers. Also try vintage radio parts or similar.
I've had, or heard of good experiences from these but there are many others (guess it's ok to post links? :) )
https://vacuumtubesinc.com (https://vacuumtubesinc.com)
http://www.findatube.com (http://www.findatube.com)
http://www.vacuumtubes.net (http://www.vacuumtubes.net)
Any idea where I can get tube socket adapters so I can run the 6b4g
-
Ebay
-
I found one 4 pin to 8 pin but it doesn't list the 6b4g as one of the tubes you can use. Will it be connected properly or is it something that needs to be custom made?
Seller is caryelectronics (14973)
Item number isNumber151166600567
Can someone verify this is correct?
Thanks
-
That would not work, the pin-outs are different. I'm weary of those sellers claiming 5Z3/80/6A3 to 5U4G/6B4G, they're just not the same. Found only one correctly listed, item no. 391676079868.
Or make your own.... ;)
-
Thanks so much that's exactly the help I was looking for! I don't know why that one didn't come up with my search. I did buy a pair so hopefully they will work out.
Maybe I'll start a new thread and ask for 6B4G recommendations.