For a frame of reference. I don't talk about it much on the forums these days. http://www.kta-hifi.net/
And I am not accepting new commissions or repair work these days.
If AVC's core magnetized (saturated many times, or DC current occurs residual magnetism), the inductance possible reduced dramatically, so the impedance would decrease to such low amount, where the preamp output not possible tolerate.
Is this the same problem as there discussed?
https://forum.intactaudio.com/viewtopic.php?f=8&t=1424&hilit=avc&start=30
https://forum.intactaudio.com/viewtopic.php?f=8&t=1424&hilit=avc&start=30
No, I don't listened music all the summer, could be some dust at the switch, I left playing music a couple of hours and will move the rotary switch to see if works ok again.
Jogged by the latest posts here I converted an 01A stage that wasn't working very well to 26. I haven't used this tube in ages, but it has a special place in my heart since it was the tube that converted me to DHTs. My jaw literally dropped when I first heard it and I muttered "this is the tube I've been waiting for all my life!"
That was back in 2011, but subsequently I bought some 10Ys and that became and still is my tube of choice. Behind that tube are the 46 (close), 47, 112A and 26. A bit further back the 2P29L. The 46 has the best piano tone and is a leaner, more percussive sound. The 26 is a little plummy on piano but wonderful on vocals. The 10Y is the master of inner detail and subtlety, including the crystal-like treble. The 26 has good treble, but not 10Y class. But nothing really matches the 10Y for all round performance. All these have been used in filament bias with Rod Coleman regs. Big chokes in the filament supply and paper in oil and DC Link caps in the PSU. I use a 1:4 step up since this stage directly feeds my 2a3 SE outputs. The Hammond 1140-LN-C is excellent - one of their broadcast range and remarkably good value.
So here's the circuit I made. I like it and it will stay in my system for a while until I miss the 10Y too much. I sometimes put in the 46 stage, which is very realistic on jazz.
That was back in 2011, but subsequently I bought some 10Ys and that became and still is my tube of choice. Behind that tube are the 46 (close), 47, 112A and 26. A bit further back the 2P29L. The 46 has the best piano tone and is a leaner, more percussive sound. The 26 is a little plummy on piano but wonderful on vocals. The 10Y is the master of inner detail and subtlety, including the crystal-like treble. The 26 has good treble, but not 10Y class. But nothing really matches the 10Y for all round performance. All these have been used in filament bias with Rod Coleman regs. Big chokes in the filament supply and paper in oil and DC Link caps in the PSU. I use a 1:4 step up since this stage directly feeds my 2a3 SE outputs. The Hammond 1140-LN-C is excellent - one of their broadcast range and remarkably good value.
So here's the circuit I made. I like it and it will stay in my system for a while until I miss the 10Y too much. I sometimes put in the 46 stage, which is very realistic on jazz.
Are you tested the frequency response of preamp?
Is LF band OK (both potentiometer and AVC version)?
See (for example):
https://www.dv-power.com/demagnetization-transformer/
Hi euro21,
I am looking at the simulation schematic in this message and trying to make sense of it...it shows a design that looks to accommodate either 26 or 01A with cCCS load and switchable filament bias according to the valve used, Rod's V7 filament regs. The switch position is consistent with 01A and indeed the valve is labeled as 01A. But it is shown with Va = 150v and Ia = 5.9 mA, both being way high for an 01A...those values might be O.K. for a 26.
Please explain, and also...what is the circuit inside the cCCS box?
I am looking to try something like this, but with the cCCS replaced by an output transformer and Slagle AVC, maybe with a different HT supply and I'm not sure about including an SSHV2 reg.
If I haven't included enough, please let me know.
Thanks for your insights and Best,
Robert
This is curious to me because 01A has the same plate structure as type 71/71A, and the filament is a single run (non-parallel) of that used in type 71.
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Which message? The 2 valves are so different I can't see why you would want to have a switch or how it would work. You could have a separate HT chassis and 2 different signal chassis containing different filament supplies and operating points that you could switch. Not too difficult.
OPT and AVC sounds nice. But if you are going to all the trouble of a build, I would 100% use a 10Y and forget any other DHTs. And do it in filament bias. You won't build anything that sounds better. Think about a separate HT chassis. Very useful and future proof. Or you could get the HT off your amp if it's a valve amp and has a little spare capacity. You could run the 10Ys at 10mA. If you don't need the gain, also consider a 6B4G or 6C4C in filament bias. To my ears a better sound than the 26.
Yes, it was a typo, from previous schematic, where #26 plate voltage was 150V.
The correct plate voltage for #01a is 127V.
As you can see in #01a datasheet, this plate current gives -about- 7.5k rp, so if you want it with choke/transformer, the required inductance -at least- must be (2*rp load) 120H (rather 3*rp 180H):
Zload>= 2*rp
Zload=2*pi*f*L (for example at f:20Hz)
The CCS is simple depletion MOSFET cascode CCS.
Be sure, that HT supply "enough good".
Transformer/choke loaded high rp tube practically unprotected to HT hum/ripple, the PSRR horrible low.
Sample:
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Thanks euro21, it would be at least LCLC...maybe another LC, or could be a SSHV2...recommendations? And I thank you for your definition of the cCCS box...I have not tried one of those, but it is on my list.
I have to admit to just listening to/enjoying the music for the last many years*, so I am way behind what most of you have done in that time,...but I have been a wary collector of parts and am happy to find the enthusiasm and desire to help from all of you here...thank you!
Andy, I have in my stash a pair of VT62 (Taylot with ceramic bases) and also 801A RCA, no 10Y, but am interested in trying this. And I do have a variable HT supply which allows switching filaments on first and HT later, I always count to 30 seconds.
All for now, too late for more, Very Best,
Robert
* Been collecting and listening to jazz LPs since the late 1950s via a Thorens TD121 purchased in early 60s with original RMG-212 with various cartridges.
The PSRR of #5277 schematic is "nothing" (only 3dB), so hum/ripple/noise on HT will be present on output about 0.7 magnitude.
If you get 10mV hum on HT, 7mV will be present on output.
It's not negligible for 2V RMS signal (case of power tube, where signal is few ten Volt, it's acceptable).
I used cLCLC for my 801a preamp HT supply (2mVpp hum on B+) ... but I use Ale's gyrator (at least 40-50dB PSRR).
IMHO OPT/choke loaded preamp requires active HT PSU.