OK,
So I have built this 813 PP amp...i like it alot, but feel the need for some more mojo in the driver stage.
Current drivers are EL34 Svetlanas , triode connected, B+ of 350V , in a choke loaded cathode follower config, RC coupled to the 813s ( 813's are at B+ of 615V) . The EL34's are driven by the phase splitter , an RCA smoked glass 6SL7GT.
I was looking at a GU50 , until I saw this video
and noticed the inside of the anode is some silver colored (metal).
And another on my sort list was Mullard EL37's (in triode) but they cost too much.
I wonder what these 807 Haltron Tetrodes would sound like https://www.trademe.co.nz/a/marketp...pment/vintage/listing/3937708870?bof=yiUoDAEr
Opinions or suggestions anyone?
So I have built this 813 PP amp...i like it alot, but feel the need for some more mojo in the driver stage.
Current drivers are EL34 Svetlanas , triode connected, B+ of 350V , in a choke loaded cathode follower config, RC coupled to the 813s ( 813's are at B+ of 615V) . The EL34's are driven by the phase splitter , an RCA smoked glass 6SL7GT.
I was looking at a GU50 , until I saw this video
and noticed the inside of the anode is some silver colored (metal).
And another on my sort list was Mullard EL37's (in triode) but they cost too much.
I wonder what these 807 Haltron Tetrodes would sound like https://www.trademe.co.nz/a/marketp...pment/vintage/listing/3937708870?bof=yiUoDAEr
Opinions or suggestions anyone?
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I’m not watching a 19 minute video. Why does this random person object to silver colored metal inside the GU50? It’s a great tube and many members here are using them.
Have you determined which driver stage is clipping first? if the 6SL7 is clipping you need a higher B+ for the 6SL7 VAS.
Also, 813 was designed to work with Kilovolts B+, my guess is you would be better off by DC coupling the EL34 to the 813 so you can drive it into grid current. Or use a interstage transformer like the Hammond 126 series in 1:2 configuration with the EL34 in triode as driver.
813 was never intended for such a low B+. The determining factor of any tetrode Push pull output stage is how much current the output tubes can deliver at low anode voltages. Thats why its possible to get crazy amounts of power with TV tubes like PL519, because they can utilize more of the B+ voltage due to their crazy high Cathode current at low plate voltages.
Also, 813 was designed to work with Kilovolts B+, my guess is you would be better off by DC coupling the EL34 to the 813 so you can drive it into grid current. Or use a interstage transformer like the Hammond 126 series in 1:2 configuration with the EL34 in triode as driver.
813 was never intended for such a low B+. The determining factor of any tetrode Push pull output stage is how much current the output tubes can deliver at low anode voltages. Thats why its possible to get crazy amounts of power with TV tubes like PL519, because they can utilize more of the B+ voltage due to their crazy high Cathode current at low plate voltages.
Thanks guys!
Both the 813's and EL34's are fixed bias. How do I DC couple el34's (or any driver tube) , to the 813's?
Might be best to start with what plate supply voltage you have and what you have for an output transformer. Also what is your desired power output.
Get some triode curves for the 813 and plot a load line.
This will help you see what sort of drive requirements you have.
The schematic in post #3 shows an example of DC coupling the driver tube as far as connection to the 813s. Notice this example has a 12bh7 driving a parallel set of 813s.
Get some triode curves for the 813 and plot a load line.
This will help you see what sort of drive requirements you have.
The schematic in post #3 shows an example of DC coupling the driver tube as far as connection to the 813s. Notice this example has a 12bh7 driving a parallel set of 813s.
Doh, I missed that in the schematic. I saw the follower stage using the 12bh7 and did not look long enough. If you need class AB2, you would omit the .22 coupling cap. Bias on the 813 would be controlled from the grid of the 12bh7.
You really want to plot a load line so you know if you need to drive the grid positive.
Attaching a pdf for the Altec 260a which is a good example of an amplifier using an 813.
Plate voltage is sort of high and output transformer is sort of high,.
You really want to plot a load line so you know if you need to drive the grid positive.
Attaching a pdf for the Altec 260a which is a good example of an amplifier using an 813.
Plate voltage is sort of high and output transformer is sort of high,.
Thanks for that Schematic. Nice looking pentode amp with independant feedback winding on the sec of the OPT . Im not sure I want to go a for a 6au6 as a driver. I want more mojo , eg dht/idht etc , perhaps a JAN Raytheon 6v6 ..i dunno
Maybe start with a schematic of what you have now as far as output transformer and power supply and also desired output power.
My higher power triode amplifiers have been mostly 811a push pull fairly close to an Altec 1570B.
Daily driver tube amplifier is currently class A using 845s.
My higher power triode amplifiers have been mostly 811a push pull fairly close to an Altec 1570B.
Daily driver tube amplifier is currently class A using 845s.
To direct couple the driver stage to the 813's you need a negative supply, at a guess something around - 120v. I wouldn't bother with pentodes as the drivers, a 6BL7 or 6BX7 would do the job or a 12BH7A or ECC99. Run them as cathode followers from a CCS, see attached 2C34 amp schematic I built for a rough idea. See also the STC 807 datasheet & application note, attached schematic.
If you want lots of power though you need more HT, at least 1kv but then you really need to know what your doing with that high voltage. I've a 1KVA toroid I wound for an 813 amp that I no longer use if your in Europe or the UK.
Andy.
If you want lots of power though you need more HT, at least 1kv but then you really need to know what your doing with that high voltage. I've a 1KVA toroid I wound for an 813 amp that I no longer use if your in Europe or the UK.
Andy.
Attachments
I have a bunch of QB2/250's waiting here, thinking of a PP-amp.
Powerdrive seems to be an alternative instead of triode drivers. AB2 aren't really nessesary as I see it, there will be enough power anyway.
Lundahl have some OPT that could work, but it's hard to find +10k Rla-a ?
I will follow this project.
/Figge
Powerdrive seems to be an alternative instead of triode drivers. AB2 aren't really nessesary as I see it, there will be enough power anyway.
Lundahl have some OPT that could work, but it's hard to find +10k Rla-a ?
I will follow this project.
/Figge