Yeah, that is an animal of a different color. Output impedance will be high and therefore its ability to drive cable and amplifier input capacitance is going to be very limited particularly with an AX, the AT or AU would work better. Too much gain for most applications IMO. Still not highly recommended. It is cute though - give it that. 🙂
It may be simple, but it would be better not to use that one. Using 12ax7s to drive cables is not a recipe for success.
Meanwhile, 2P29L with Ale's anode module, a transformer, or choke (or even resistor) load, combined with a source (or cathode, or emitter) follower will be very satisfying.
I've been comparing my "pretty good" 2P29L preamp to my 112A preamp and the 112a is clearly better, so the 2P29Ls are going back in the cupboard. I've rebuilt the 2P29L preamp into a 112A preamp and it sounds really nice. I always regarded the tube as a poor cousin of the 01A but there's a lot more to it than I thought. Not cheap anymore and harder to find in Europe. OK if you're in the USA.
To Andy's point I also preferred the 12A/112A to the 26 and 226/326. The lower rp was a better match the HA-133 plate to line transformer in the original line stage. That unit has been gone a long time, currently using EML20B into Monolith Magnetics 20K:150/600 plate to line transformer.
They don't really compare, the Monolith outclasses the HA-133 in every way. more bandwidth, lower distortion, rated for 30mA operating current, etc. Subjectively and IMO they are more transparent and more extended in both the HF and LF regions. I did a lot of measurements, but this is 6 years ago and I can't easily locate them otherwise I'd share them here. The real point is that I recommend Monolith Magnetics without reservation, and they have provided line to plate, IT, power, and output transformers for most of my projects over the past 6 years. (I have also used them in projects I built for several friends including two EML20 based line stages, and a 4 chassis GM70 stereo pair.)
From my experience and others, the hum of these tubes goes down tremendously if the tubes are shielded. Has anyone found any shields that were made for this size tube? Alumimum foil works, but looks terrible!
I love the Goat shields, but I can never find any that fit this tube. Would love to find a vintage shield that looks good.
I love the Goat shields, but I can never find any that fit this tube. Would love to find a vintage shield that looks good.
Look for reproductions of the Western Electric tube shields. I found some on eBay in the past. Other sources are antique radio shows and hamfests.
Thanks, I'll keep an eye out for WE tube shields. I actually have a 71a, but 26 and 71a appear to be the same tube size.
Maybe I'll try some of the antique radio or ham radio boards. Thanks for the suggestions. I'm not aware of any in-person antique radio or hamfest shows, but will look. Thanks!
I am using a very similar material in my EML20B line stage to what Andy has recommended above. It works very well.
Valuable recommendation, especially considering your Lundahl background.
Please don't confuse me with Kevin Carter 🙂 I have no affiliation with Lundahl, although I do use a lot of their transformers for inputs and SUTs.
No.
Usually AVC/TVC requires only AC (no airgap). If DC current flow via its, the core saturating.
Use the AVC as part of a parafeed arrangement with a suitable choke load on the plate of your dht, a blocking capacitor from plate to AVC.
I use the AVC after the Ale's Gyrator with output capacitor for years without problem but a couple of days ago the sound become distorted like no bass & with quick cutoffs, all the summer don't listened music....
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