I've been using 4P1L as PP driver in my GM70 PP amplifier and like the sound. I used it in place of 46 as they are hard to get. The 4P1L is transformer coupled to the GM70.
As usual the 4P1L is very microphonic and that is beginning to concern me. I'm not entirely sure if it makes a difference but if the music is loud and cut off suddenly (lifting the cartridge off the record) a ringing can be heard that fades out; like a small bell.
I'm looking for suggestions for an alternative that is relatively easy to get, not too expensive. Preferably directly heated but I might have to concede on that.
As usual the 4P1L is very microphonic and that is beginning to concern me. I'm not entirely sure if it makes a difference but if the music is loud and cut off suddenly (lifting the cartridge off the record) a ringing can be heard that fades out; like a small bell.
I'm looking for suggestions for an alternative that is relatively easy to get, not too expensive. Preferably directly heated but I might have to concede on that.
Thanks Ale. I have 2P29L in my stash from what you have written about already. I was going to use them in my line amp where now it is 12B4A. Trying to get the DHT thing further back in the chain. Maybe I should try it in the GM70 first. That will then raise the question what will I use in the line in future? But that's another day.
Cheers,
Stephen
Cheers,
Stephen
The 2P29L can swing the volts you need, it’s not microphonic at all and has good current drive (not as much as 4P1L). Will do a good job I think.
It will be easy to adapt in your circuit it looks like.
For line stage, it will depend on how much gain you need. A good solution is to have a good step down transformer (e.g. 4:1). That helps with the microphonic noise of some DHTs and also reduces the gain if this is too much of an issue. There are many good candidates out there including 26, 01a, 801a, 10Y, etc. Of course the 2P29L is great for preamp if sourcing the valve and cost is a concern, then you can use it in both stages.
Ale
It will be easy to adapt in your circuit it looks like.
For line stage, it will depend on how much gain you need. A good solution is to have a good step down transformer (e.g. 4:1). That helps with the microphonic noise of some DHTs and also reduces the gain if this is too much of an issue. There are many good candidates out there including 26, 01a, 801a, 10Y, etc. Of course the 2P29L is great for preamp if sourcing the valve and cost is a concern, then you can use it in both stages.
Ale
With 12B4-A and the 4.5:1 step down I have 0 gain and while good for 95% of the time, now and again if I want it super loud, it's not enough. I did have 6N6P in there and that was a bit too much gain and the 12B4-A were a lot nicer sounding.
My only concern was cascading two valves of the same type but maybe that's a prejudice I can slay. It too is differential like Lynn Olson's Raven. Your other suggestions while no doubt good ones, make me wonder how suitable they would be in that circuit.
My only concern was cascading two valves of the same type but maybe that's a prejudice I can slay. It too is differential like Lynn Olson's Raven. Your other suggestions while no doubt good ones, make me wonder how suitable they would be in that circuit.
I believe the 12P17L is electrically equivalent, or very close, to the 4P1L except for heater voltage and the fact that it's indirectly heated. I don't know if it has the same issues with microphonics or not. Perhaps others can comment on that aspect.
Never tried either in a preamp but I just started working on building an amp and I'll be using one of those types.
I used the 12B4A also, some years ago. It sounded good too, nice and full, but also had issues with microphonics. I tried the 2P29L when I was breadboarding preamps last year. I liked it and it was not microphonic. I ended up using 1626s, which I preferred, after reading Andy Evans' comments about them over the years.
Never tried either in a preamp but I just started working on building an amp and I'll be using one of those types.
I used the 12B4A also, some years ago. It sounded good too, nice and full, but also had issues with microphonics. I tried the 2P29L when I was breadboarding preamps last year. I liked it and it was not microphonic. I ended up using 1626s, which I preferred, after reading Andy Evans' comments about them over the years.
Reading this thread one could get the impression that tubes/valves were only made in the US and the USSR. This is not true of course, a lot of wonderful tubes were also made in Western Europe, but they don’t often get the attention they deserve. For line amp duty my favourite is the Marconi Osram LP2 (equvivalents are CV1166, Lp220 etc.). It has an unusually high amplification factor for this kind of lowish plate impedance early battery tube ( mu 15, impedance 4KOhms). It’s perfect with filament bias and transformer stepdown output. I use it with an LL1660 4,5:1 and I get just enough amplification for my needs. You have to damp the tube socket a bit, but in my experience the microphony actually goes away after a few months. In the not too distant future I’ll build a Tungsram P15/250 power amp!
The main issue for most of us is rarity, cost and quality of our European heritage. I have a few good 220 and am keeping them for a rainy day, but now they really aren't available much and there's a lot of emphysemic old tat amongst old globes for sale. Russian and US stock seems to hold up better. Thoughts?
For line stage preamp purposes, I have a personal preference for 01a. However, the 2P29L works perfectly and sounds really nice. A bit more on the expensive side you can use 10Y/VT-25 and 801a. Tungsten filaments have something special, you can hear the difference. Of course you can go down the exotic route, I played with German or British valves, but it all depends what you can get. Also, these DHT valves are very old devices and unless you can source NOS valves, it can be a bit of hit and miss. There are various ways to tame the microphonic noise, however there are some valve devices which are horribly microphonic and will drive you crazy. Dampening, thick top plates and step down transformers are good ways of dealing with it.
You won't go wrong with any of the valve types mentioned.
Cheers
Ale
I understand that microphonics is an issue with the 4P1L when used in a preamp but what about in an amp? Any less of a problem there?
And how does the 12P17L compare, in terms of microphonics, in either preamp or amp use?
I was pleasantly surprised at the lack of microphonics in the 2P29L. Surprised because it is both directly heated and considered a "battery tube" because of the very low filament voltage.
It seems these "battery tubes" have filaments that are very sensitive to vibration. I tried a few when I was breadboarding and the worst, in one sense, was the 1LE3. I tried it after reading positive comments about a build someone did many years ago. It was so sensitive that lightly rubbing a fingertip across the volume knob could be heard thru the speakers. Yikes!
I added, "in one sense", above because I actually heard no indication of microphonics while playing music and there was no ringing when the music stopped. And the breadboard was on the same table as the speakers, right between them and only about 18" or so (.5m) away. Of course, tapping them or the table was also audible.
The 4P1L are in my power amps as input/driver to the GM70s. They are very microphonic in general although the odd one is OK.
I'm not sure what to hear if they affect the music as I'm loving the sound but now and then, if playing loud, lifting the arm off the record can result in the ring being heard as if the valve is being pinged. I don't know if that's an external thing or an external thing exciting the internals. I could be worrying about nothing; that's a possibility as many DHTs are microphonic I'm led to believe apparently.
In the power amps, the 4P1L is being run flat out however if it was in my line stage, I have a 4.5:1 step down and an AVC after that so it might be an idea to run the 4P1L in the line and they would live inside the box and the 2P29L as GM70 driver.
I'm not sure what to hear if they affect the music as I'm loving the sound but now and then, if playing loud, lifting the arm off the record can result in the ring being heard as if the valve is being pinged. I don't know if that's an external thing or an external thing exciting the internals. I could be worrying about nothing; that's a possibility as many DHTs are microphonic I'm led to believe apparently.
In the power amps, the 4P1L is being run flat out however if it was in my line stage, I have a 4.5:1 step down and an AVC after that so it might be an idea to run the 4P1L in the line and they would live inside the box and the 2P29L as GM70 driver.
Do you need the preamp to drive a long cable? Just wondering how you could proceed if the preamp and amp were next to each other and you didn't need a step-down. The GM70 has a mu of 6.7 on the data, though I don't know if this would be true at your operating point. I've used the LL1660 just as a plate choke in 1:1 in 2-stage amps. With a driver tube with a mu of around 20 you may have enough gain if you have sensitive speakers. Thinking of valves like EL84, EL41 and KT61 in triode for instance. I was for many years resistant to using anything other than DHTs but being able to use 2 stages rather than 3 tended to clean up the sound enough to be worthwhile. I mention the above medium power tubes as being beefy drivers for the output stage - they can take decent current.
The cables are longish. I like low Z drive to diminish the effects of cables. The line only needs moderate gain. The amp is low gain as I have reasonably efficient speakers. Driver needs to have a mu around 10. For full power the input is about 7V but I don't need full power or even near it but the headroom makes for a big relaxed sound with no strain.
I believe the EL84 makes a nice triode driver as does 6V6 from what I've read. However being new to DH valves, there is something that I'm finding quite attractive about the sound. This is my first power amp and likely my last.
OTOH, maybe it's the use of medium power valves as drivers that's giving me the sound I'm hearing. Hard to know without experimenation hence this thread to gauge ideas of those that might have done something like this.
Cheers,
Stephen
I believe the EL84 makes a nice triode driver as does 6V6 from what I've read. However being new to DH valves, there is something that I'm finding quite attractive about the sound. This is my first power amp and likely my last.
OTOH, maybe it's the use of medium power valves as drivers that's giving me the sound I'm hearing. Hard to know without experimenation hence this thread to gauge ideas of those that might have done something like this.
Cheers,
Stephen
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