transmitter tube amp - Page 3

Tweeker · 29th October 2006, 09:48 PM

Western Electric 43A theatre amplifier schematic from Nutshell High Fidelity. Note the 211 triodes used as rectifier diodes and another pair as final stage.

Tweeker · 29th October 2006, 10:02 PM

Quote:

I have found this http://www.tube-fullmusic.com/produ...roduct0-805.htm It seems the curve of a pentode
do these tubes normally work in class A2 or AB2 (with grid current) ?

These are the grid current curves, not plate current is why they have thier shape. Yes, the 805 tube is normally used with grid current. Class B(2) amplifier/modulator or class C amplifier/oscillator use would be the norm in thier original typical usage.

sparky813 · 30th October 2006, 02:58 AM

I have both the types of tube solckets for the 212's, the horizontal chassis mount and the vertical front panel mount as shown in the rack panel above. I thought 813's were overkill enough, but I guess I'll try something with the 212's. My 212's were used originally in a theater amp. Thanks for all the info. The web is still amazing.

Sparky

7N7 · 30th October 2006, 07:46 AM

Tweeker:

Thanks so much; that sort of stuff is a real treat for me to see.

Anyone got a picture of John Logie Baird's TV set up? I read that because his system needed so much light, he had some enormous arc lamps driven by "a pair of enormous triodes running at 15,000V". I have no idea why one would drive arc lamps with triodes, but perhaps the light was more hi-fi?

As for the 955s, as there is some interest, I will look for the test results of my experiments.

I would not have thought of 955 as the right valve for phono. I think it's best to have some decent gm, hence the popularity of 417A/5842 etc. Choices would be EC8010, perhaps 6GK5 and one or two others like 437A or EC8020 for the rich. I did some work using the 416D planar triode (mu 250 gm 65), which would have worked probably but was tricky. I would quite like to have tried D3A triode strapped. Mu is 85, with gm up to 40 and Ca-g is only 2.7pf in triode mode.

Paul

7N7 · 30th October 2006, 08:02 AM

849A looks good for big SE fans, provided they fancy building a 2.5kV power supply.

82W at 3% distortion is very impressive.

Paul

Gold_xyz · 30th October 2006, 11:46 AM

Quote:

Originally posted by Tweeker
These are the grid current curves, not plate current is why they have thier shape. Yes, the 805 tube is normally used with grid current. Class B(2) amplifier/modulator or class C amplifier/oscillator use would be the norm in thier original typical usage.

hi Tweeker

This graph seems me different from the original datasheet...
http://frank.pocnet.net/sheets/111/8/805.pdf

( from the http://www.tube-fullmusic.com/produc...oduct0-805.htm )
Y axis = Ia anode current ?
X axis = Ua anode voltage
Curves = Ug grid voltage

update..
perhaps is the axis x more expanded...

bye

Bandersnatch · 30th October 2006, 11:18 PM

Hey-Hey!!!,
My 813 project is comming along. B+ of ~650, U-L at 37.5% thanks to a custom pair of output TX's. They deserve a bit of space...

I acquired a Peerless S-271-S, and had it unwound. It is a 2.25" stack of 1.75" EI rated for 80W. It has 8 layers of primary on each side of CT, so I get end-of-layer taps at any multiple of 12.5%, so I'm getting them wound with the first three layers tapped. Stacked with .009" M3.

The circuit is a pentode( or faux pentode cascode ) diff amp. CCS by MOSFET and a E-Linear connection to 25% taps( each half of the diff amp attached to the side of the OPTx that it is feeding the g1 to). Gapped C-core grid choke to side-step the 30k grid circuit limit.

B+ is done LC-LC with 10 Hy and parallel damper diodes and 660vac PIO caps. ~150 mA per 813 idle. With a 5k a-a load, and 37.5% U-L it will still be Class A, and as such ought to deliver me power on par with the output's rating. I can always have another coil wound for additional stacking of Iron if it turns out I need more core area.
cheers,
Douglas

sparky813 · 31st October 2006, 01:10 AM

Bandersnatch, It sounds very interesing. I don't understand very much of what you posted, but can you post a schematic at least of the audio circuit, especially the UL taps and feedback arrangement. Thanks.

Sparky

Bandersnatch · 31st October 2006, 10:32 AM

Hey-Hey!!!,
I will direct you to an already published schematic.

http://www.audioroundtable.com/Group...cts/Merlin.pdf

That is the nuts an' bolts of it.
cheers,
Douglas

sparky813 · 31st October 2006, 02:53 PM

Hey Bandersnatch,

Thanks for the schematic. How do you achieve CCS1 and CCS2 and are they really necessary? It seems like resistors would be o.k. here as well for the bias blocking inductor. I am trying to understand the precise advantages of Douglas Piccard's schematic.

Please post your results when the amp is done. It will be most intersting. I plan to do the same.

Sparky

29th October 2006, 09:48 PM	#21
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	Western Electric 43A theatre amplifier schematic from Nutshell High Fidelity. Note the 211 triodes used as rectifier diodes and another pair as final stage. __________________ Be sure your foil hat has a good low impedance ground.

30th October 2006, 07:46 AM	#24
7N7 diyAudio Member Join Date: Jan 2003 Location: England	Tweeker: Thanks so much; that sort of stuff is a real treat for me to see. Anyone got a picture of John Logie Baird's TV set up? I read that because his system needed so much light, he had some enormous arc lamps driven by "a pair of enormous triodes running at 15,000V". I have no idea why one would drive arc lamps with triodes, but perhaps the light was more hi-fi? As for the 955s, as there is some interest, I will look for the test results of my experiments. I would not have thought of 955 as the right valve for phono. I think it's best to have some decent gm, hence the popularity of 417A/5842 etc. Choices would be EC8010, perhaps 6GK5 and one or two others like 437A or EC8020 for the rich. I did some work using the 416D planar triode (mu 250 gm 65), which would have worked probably but was tricky. I would quite like to have tried D3A triode strapped. Mu is 85, with gm up to 40 and Ca-g is only 2.7pf in triode mode. Paul __________________ Plug them in and light them up

30th October 2006, 08:02 AM	#25
7N7 diyAudio Member Join Date: Jan 2003 Location: England	849A 849A looks good for big SE fans, provided they fancy building a 2.5kV power supply. 82W at 3% distortion is very impressive. Paul __________________ Plug them in and light them up

30th October 2006, 11:18 PM	#27
Bandersnatch diyAudio Member Join Date: Jul 2003 Location: Ann Arbor, MI	Hey-Hey!!!, My 813 project is comming along. B+ of ~650, U-L at 37.5% thanks to a custom pair of output TX's. They deserve a bit of space... I acquired a Peerless S-271-S, and had it unwound. It is a 2.25" stack of 1.75" EI rated for 80W. It has 8 layers of primary on each side of CT, so I get end-of-layer taps at any multiple of 12.5%, so I'm getting them wound with the first three layers tapped. Stacked with .009" M3. The circuit is a pentode( or faux pentode cascode ) diff amp. CCS by MOSFET and a E-Linear connection to 25% taps( each half of the diff amp attached to the side of the OPTx that it is feeding the g1 to). Gapped C-core grid choke to side-step the 30k grid circuit limit. B+ is done LC-LC with 10 Hy and parallel damper diodes and 660vac PIO caps. ~150 mA per 813 idle. With a 5k a-a load, and 37.5% U-L it will still be Class A, and as such ought to deliver me power on par with the output's rating. I can always have another coil wound for additional stacking of Iron if it turns out I need more core area. cheers, Douglas __________________ the Tnuctipun will return

31st October 2006, 10:32 AM	#29
Bandersnatch diyAudio Member Join Date: Jul 2003 Location: Ann Arbor, MI	Hey-Hey!!!, I will direct you to an already published schematic. http://www.audioroundtable.com/Group...cts/Merlin.pdf That is the nuts an' bolts of it. cheers, Douglas __________________ the Tnuctipun will return


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30th October 2006, 02:58 AM	#23
sparky813 diyAudio Member Join Date: Oct 2006	I have both the types of tube solckets for the 212's, the horizontal chassis mount and the vertical front panel mount as shown in the rack panel above. I thought 813's were overkill enough, but I guess I'll try something with the 212's. My 212's were used originally in a theater amp. Thanks for all the info. The web is still amazing. Sparky

31st October 2006, 01:10 AM	#28
sparky813 diyAudio Member Join Date: Oct 2006	Bandersnatch, It sounds very interesing. I don't understand very much of what you posted, but can you post a schematic at least of the audio circuit, especially the UL taps and feedback arrangement. Thanks. Sparky

31st October 2006, 02:53 PM	#30
sparky813 diyAudio Member Join Date: Oct 2006	Hey Bandersnatch, Thanks for the schematic. How do you achieve CCS1 and CCS2 and are they really necessary? It seems like resistors would be o.k. here as well for the bias blocking inductor. I am trying to understand the precise advantages of Douglas Piccard's schematic. Please post your results when the amp is done. It will be most intersting. I plan to do the same. Sparky

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