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Old 1st October 2015, 03:27 PM   #1
rol is offline rol
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Arrow All DHT single-ended 211 amp suggestion?

I am closing on the C3m-300B-GM70 amp, and planning ahead for another big triode that I've always fascinated, the 211. It will be a 3 stages, all DHT amp. I want to make use of what I have on hands so any suggestions on the best configuration is appreciated. Right now I have in my drawer the 10Y, 45, 46, 71A, 26 and 6F8G(not dht, but would definitely use them if needed). The driver tubes will be connected via an interstage transformer.

What I have on mind is 10Y -> 45 -> I.T -> 211. Is there any better choice that you could suggest me?

Thanks
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Old 1st October 2015, 03:39 PM   #2
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Hi Rol

You can try find lots informations about all dht amplifiers

on this Thomas Mayer excellent blog in 211 section.

VinylSavor

http://vinylsavor.blogspot.com/search/label/211

Hope this inspire your diy work
Have a nice day
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Old 1st October 2015, 04:43 PM   #3
euro21 is offline euro21  Hungary
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Quote:
Originally Posted by rol View Post
What I have on mind is 10Y -> 45 -> I.T -> 211. Is there any better choice that you could suggest me?
Do you want to take advantage of A2 region?

I use in my 801a/VT62 PSE 841->cascode CCS->C->cCCS loaded 10Y CF driver up to +30V bias (up to 150Vpp grid swing). In this region 801a grid current only 4-5mA, so 10mA is acceptable with 30mA (10Y) bias current.

As you can see in 211 datasheet at +50V grid current would be even 22mA! This is a big challenge to driver tube/semiconductor/interstage. :-)

Assistance with 211 powerdrive type design

IMHO interstage is not the best solution to driving "grid current hungry" tubes.
Driving (1:1) IT with enough large (30-50mA) primer current is not cost effective project. :-)
For me cathode follower (CF) or FET source follower is more feasible than IT driver.

If you want 2.5 stage (VAS+CF+output tube) amplifier, as VAS device not so many DH tubes can enough large gain. I use 841/VT-51, and tried EML20 DHT tubes in the first stage.

Also tried russian 4P1L DHP (pentode) as triode with very good experiences, but gain is not so much to drive output tube with large (180-200Vpp) gate swing (as 211).

Vinylsavor's solution is very elegant.... with 1:4 input transformer. :-)
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Old 1st October 2015, 05:04 PM   #4
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I'd go 26 to 46 (or 45) and then source follower driving the 211 grid.

Look up Ale Moglia's distortion comparison table. The 46 is quite linear!
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Old 1st October 2015, 05:08 PM   #5
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I have draws full of DHTs, all the usual suspects. I use 4P1L because it sounds as good as any of them. More dynamic and better treble than 26, more gain than 10Y or 46 (both good), low Ra and cheap as chips. The virtue of using it is you can use it in filament bias with Rod Coleman's regulators, and that eliminates cathode bias caps. Voila.
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Old 1st October 2015, 06:59 PM   #6
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Quote:
Originally Posted by euro21 View Post
Do you want to take advantage of A2 region?

I use in my 801a/VT62 PSE 841->cascode CCS->C->cCCS loaded 10Y CF driver up to +30V bias (up to 150Vpp grid swing). In this region 801a grid current only 4-5mA, so 10mA is acceptable with 30mA (10Y) bias current.

As you can see in 211 datasheet at +50V grid current would be even 22mA! This is a big challenge to driver tube/semiconductor/interstage. :-)

Assistance with 211 powerdrive type design

IMHO interstage is not the best solution to driving "grid current hungry" tubes.
Driving (1:1) IT with enough large (30-50mA) primer current is not cost effective project. :-)
For me cathode follower (CF) or FET source follower is more feasible than IT driver.

If you want 2.5 stage (VAS+CF+output tube) amplifier, as VAS device not so many DH tubes can enough large gain. I use 841/VT-51, and tried EML20 DHT tubes in the first stage.

Also tried russian 4P1L DHP (pentode) as triode with very good experiences, but gain is not so much to drive output tube with large (180-200Vpp) gate swing (as 211).

Vinylsavor's solution is very elegant.... with 1:4 input transformer. :-)
hi,
i will building and starting
how about used 811A --- IT (1:1) ---- 211.?
can you give suggestion of that?

regards
ed
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Old 1st October 2015, 07:51 PM   #7
Gluca is offline Gluca  Italy
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801A and 211 with stacked supplies. input transformer if you need more gain.
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Old 2nd October 2015, 01:31 PM   #8
indra1 is offline indra1  Indonesia
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Quote:
Originally Posted by suwaned View Post
. . . how about used 811A --- IT (1:1) ---- 211.? . . .
Halo pak Edy. 811A will require a pre buffer due grid current at zero bias or class A2 operation and the IT will have to be at least 15k:15k. I think 812A or 3C24 will be easier due class A1 operation and 8k:8k IT may be sufficient. However, due to the high Ra of the tubes mentioned, careful implementation is critical (not easy) for satisfactory low frequency response.
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Old 2nd October 2015, 01:55 PM   #9
kaputt is offline kaputt  Germany
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Originally Posted by Gluca View Post
801A and 211 with stacked supplies. input transformer if you need more gain.
+1
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Old 2nd October 2015, 05:31 PM   #10
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Quote:
Originally Posted by indra1 View Post
Halo pak Edy. 811A will require a pre buffer due grid current at zero bias or class A2 operation and the IT will have to be at least 15k:15k. I think 812A or 3C24 will be easier due class A1 operation and 8k:8k IT may be sufficient. However, due to the high Ra of the tubes mentioned, careful implementation is critical (not easy) for satisfactory low frequency response.
halo juga Pak Indra, nice meet with you in here.
thank you for suggest.
some time i will learn and ask about that to you..
last day when we discus, give me more information about transformer .
i have already for my 211 project,
HW rectifier 866A x2 for HV supply and DIY PT from Pak Ruby.
and i still waiting 2.5v 12A for PT filament.

20150919_182419.jpg

regrads
ed
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