For me it's too much.
This curve represents -3dB at 26kHz, and about -8dB hole at 45kHz, so phase changing will be considerable over 10kHz.
Commercial transformers has several resonances, but -if they properly designed and sufficiently loaded- this resonances mostly over 100-150kHz.
Try to compensate 45kHz collapsing with R//C circuit (33k//few hundred pF).
The first picture is my -Ale's gyrator loaded- 801 preamp curve: -1dB 10Hz..85kHz.
(21mA compensated...).
The second picture is my daily used (CCS loaded, C coupled) #26 preamp measuring.The 65kHz "bump" is due to my -parafeed coupled- 400H S&B TVC.
Attachments
15k:600 is 5:1 turns ratio.
If you have 3.5 db gain:
3.5=20*log(Uoutput/Uinput)
U2/U1 equal about 1.5, aka at 2V output you need 1.337V preamp input level. The OPT primary level is 10V.
15k:150 is 10:1 turns ratio. You have 10V on primary, so 1V on secondary, so gain about -2.5dB (at the same input level as case of 15k:600).
Thanks, that's easy enough to try. I have plenty of small polystyrene caps. I also have a TVC (Sowter) that I can try on the output, but of course that puts 2 transformers in series.
****
euro 21
What do you use in your CCS ??......DN2540 x 2 ??......have you tried combinations of other devices ??.....appreciate if you could share your experience with CCS loading to get such a performance please.
Cheers,
King
Have you tried other FET devices, other than DN2540 at the lower location.....something like BF862....2SK170....etc....etc.....
If not, why not.....or because you think they won't make a big difference in the musical performance of the amp anyway ??
*****
I am still using and enjoying my line amps built according to your suggestions !!
Thankyou very much.......
Happy New Year mate....!!!
King
If not, why not.....or because you think they won't make a big difference in the musical performance of the amp anyway ??
*****
I am still using and enjoying my line amps built according to your suggestions !!
Thankyou very much.......
Happy New Year mate....!!!
King
'26 linestage
Hi,
My reference preamp for over 15 years has been the Ronan 26 preamp.
I lived with hum for many years, I got used to it. The dynamics were worth it. Did you try shielding the tubes? Of course, part of the reason to build a globe tube anything is to see the tube, but the 26 doesn't really glow much.
I stumbled on this total solution by putting a piece of 3" dryer vent pipe around one tube, I just set it on the amp end up. It totally quieted down. I found another piece of dryer vent pipe and total silence!!
This may not be the problem but you should try it. 1920s radio RF sections are a good source for this type of shield.
I also notice that some 226 and 326 and 426 are very microphonic and pick up the vibration from the power transformer or choke. That would also sound like filament hum, both at 120HZ I think.
Have fun!
John
Hi,
My reference preamp for over 15 years has been the Ronan 26 preamp.
I lived with hum for many years, I got used to it. The dynamics were worth it. Did you try shielding the tubes? Of course, part of the reason to build a globe tube anything is to see the tube, but the 26 doesn't really glow much.
I stumbled on this total solution by putting a piece of 3" dryer vent pipe around one tube, I just set it on the amp end up. It totally quieted down. I found another piece of dryer vent pipe and total silence!!
This may not be the problem but you should try it. 1920s radio RF sections are a good source for this type of shield.
I also notice that some 226 and 326 and 426 are very microphonic and pick up the vibration from the power transformer or choke. That would also sound like filament hum, both at 120HZ I think.
Have fun!
John
Phosphor bronze mesh with brass brazing rod springs to hold it on, earthed.
Steel plate under the shelf above, earthed.
Copper foil covering the shelf below, earthed.
Hum no longer a problem.
Steel plate under the shelf above, earthed.
Copper foil covering the shelf below, earthed.
Hum no longer a problem.
An externally hosted image should be here but it was not working when we last tested it.
Yes and the 26 is a great sounding valve and in my personal opinion a great contender to the 01a. If you ask around and read the various threads you will find the 26 to be one of the favorites amongst the 01a, 4P1L and 10Y. I recently built a new preamp with the C-99/CX-299 which surprised me a lot. It also has thoriated tungsten filaments and is a very old and hard to find valve. Most of the DHTs perform really well on line stages, there are small differences between them when loaded with a gyrator.
Cheers, Ale
Cheers, Ale
Exactly as above. I haven't directly compared the 26 and 01A with a gyrator, but with interstage like the LL1660 I have built both and they're both good. You can also make a case for 4P1L and 10Y as Ale states. But also a few other DHTs that nobody talks about like the 1G4G which I have in some interesting tall bottles and have used and liked before, or even the humble 3a5 which has a usefully higher mu.
46 and 71A are interesting but not so straightforward in filament bias, while 30 and 31 are less interesting unless they are some of the rarer globes or tall thin bottles I was referring to in my collection and which I really should try one day. I also have a few types like the 12A which I can't really see much use for when the 26 and 01A are so nice, but all DHTs like this are going to be better than the usual go-to 6SN7s and other commonly used indirectly heated tubes, especially gyrator loaded and in filament bias.
That's good because I have MANY spare 26 tubes that needs to be used. A 26 preamp with full amplification would greatly simplify the input stage of the following power amp. However I have built a 26 preamp before but that was with transformer output. I'm just a bit sceptical as to how much the mu-follower of the gyrator would change the sound relative to transformers.
In a direct comparison with LL1660 and LL1635 interstages I preferred the gyrator. Lower output impedance is also a massive plus factor, since I don't use step-down at all and don't want to lose any gain. I have 2 stages in total from my DAC - my outputs are PSE 4P1Ls and in my smallish room I can feed them with 01A, 26 or 4P1L as long as I have 2v or so coming from the DAC. If you need the gain, use 2 stages with gyrator loading like 26 into 26 and then the outputs of your choice - 4P1L, 2a3, 300b, whatever. You could run the 26 at 6mA or 7mA to get a bit more drive, or ideally use a 4P1L at 25mA as second stage. Not at all expensive and a brilliant tube.
Frankly I don't see the point - you're paying more for less then with a gyrator. I have a few Lundahl interstages I no longer use. For the 01A you just need a 5mA gap. In fact, if the PP interstages from Lundahl and maybe others are gapped for 5mA anyway, they might also work.
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