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Old 19th March 2003, 02:29 PM   #1
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Default 845 or 813 valves at 600V?

At lunch time today I was asked which valve would sound best at 600V - an 845 or triode mode 813?

I don't have experience with either valve (I have a pair of 845 but haven't done anything with them...). Looking at their curves I can't see that it makes a lot of difference... Has anyone any experience with these valave at an OP of, say, 600V and 100mA.

Actually I think at this OP the higher gain of the 813 means it probably wins but I could be completly wrong - again

Any help would be appreciated.

ciao

James
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Old 19th March 2003, 03:04 PM   #2
SY is offline SY  United States
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That's an odd question, much akin to, "What's better for opening a can, a screwdriver or a pair of pliers?" Hey, how about a CAN OPENER?

These are fine tubes for HV/low current circuits. Why use an inappropriate component for a given set of conditions? If you want to use an 813, use a power supply with a comma in the output.
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Old 19th March 2003, 03:25 PM   #3
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Hi SY,

It is and it isn't an odd question...

It came about as we were discussing valve RIAA pre-amps and one of my engineers remarked that "using valves in an RIAA pre is odd - I can understand the choice in a power amp. but why for low level signals that need lots of equalisation?" A very fair question and one I was happy to take on (he's still not convinced...). But that lead onto the most outrageous valves used in an RIAA pre .. and hence to the 845 RIAA amp with the 845 run with a 600V B+. Then another collegue opinioned that the 813 in triode mode was more linear at 600V than an 845 so it would be a better choice. I think he was playing 'devils advocate' but I have no way of deciding one way or the other as the plate curves for both look very similar and I have no other data for an 813 in triode mode...

Curiosity drove the question - please don't kill the cat

BTW - what valve in triode mode would you recommend at 600V? I'm not sure what I would recommend at that voltage for a power amp or pre-amp. Maybe a Monkey style design would work best at that B+?

ciao

James.
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Old 19th March 2003, 03:38 PM   #4
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In my own triode amp, I'm using 6LF6s driven in enhancement mode (i.e., grounded grid, input to screen). But I've had good luck with 6550As triode strapped and EL34s ditto at similar plate voltages. There are no doubt a lot of other choices. I don't know what the max plate voltage rating of 300B is...

FWIW, I use tubes in my RIAA, but nothing commonly available. In such circuits, passive eq is the way to go, IME.
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Old 19th March 2003, 03:58 PM   #5
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Quote:
In my own triode amp, I'm using 6LF6s driven in enhancement mode (i.e., grounded grid, input to screen). But I've had good luck with 6550As triode strapped and EL34s ditto at similar plate voltages. There are no doubt a lot of other choices. I don't know what the max plate voltage rating of 300B is...
6LF6s looks interesting. I'd forgotten all my 509 and 519 experience too.

600volts is beyond the manufacturers recommended Va for triode mode 6550 or El34s so I've never run them that hot. 300B normal max is 450V so it makes a good Monkey at 600V or so.

I agree with the passive eq. on RIAA. At present mine is still transistor - though it does run off +/-60V rails to keep things nice and linear I'm trying to source some 6F12s to build a replacement...

ciao

James
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Old 19th March 2003, 04:34 PM   #6
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Quote:
Originally posted by James D.


It came about as we were discussing valve RIAA pre-amps and one of my engineers remarked that "using valves in an RIAA pre is odd - I can understand the choice in a power amp. but why for low level signals that need lots of equalisation?" A very fair question and one I was happy to take on (he's still not convinced...). But that lead onto the most outrageous valves used in an RIAA pre .. and hence to the 845 RIAA amp with the 845 run with a 600V B+. Then another collegue opinioned that the 813 in triode mode was more linear at 600V than an 845 so it would be a better choice. I think he was playing 'devils advocate' but I have no way of deciding one way or the other as the plate curves for both look very similar and I have no other data for an 813 in triode mode...
Hi James, all

Did someone say 813 ?

I have tried the 845 and the 813 in the same amps , started with 845s and ended with
813s , but that is at high voltage, never tried either at low voltage, so can't really say which is "best" at 600V
To my ears most of the valves I have tried sounds best wide open, high voltage,
they seem to open up , but that is probably a taste thing.
But as a guess , at 600V , maybe the 845. Or maybe not.

Using transmitter valves in a RIAA pre sounds , but why not go all the way
and use them at 1100 volts ?
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Old 19th March 2003, 04:47 PM   #7
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Default 813 as a Triode

I have been running a p-p 813 triode amplifier since 1997.

Admittedly I am using 830V (7k a-a). 813 is great value.

At 100mA ra is about 1.8k - i.e. the same as an 845, but becasue mu of 813 is 8, I need only about -75V bias which makes it much easier to drive.

The filament supply is a pain though: 10V @ 5A; I am therefore burning 100W just to light 'em up - and they do look lovely lit up.

I have attached triode curves for 813.

7N7
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Old 19th March 2003, 04:50 PM   #8
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No doubt given the current 6LF6 pricing/availability, I'll be moving over to 509/519 when the time comes to retube.

IIRC, both the 6550 and the EL34 are rated to 600V plate (data sheets for 6CA7 indicate 800V max with no current for both plate and screen). The screen ratings are lower, but only for pentode and UL connections where plate and screen don't track.
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Old 20th March 2003, 08:10 AM   #9
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Hi Slowmotion,

Thanks for your reply, I seem to remember that the 600V point was chosen as it worked better as a pre-amp at that point... I think I need to go re-read some of my bumf...

Hi 7N7,

Yeah the 813 looks very nice at lower voltages and it's extra gain against an 845 or 211 looks useful. Not to mention that it is cheaper too...

Hi SY,

Agree with the 600+V in pentode or tetrode mode but GE state max 500V in triode GE 6550A data

I can't find my EL34 data but I recall a similar limit in triode mode. Of course, being valves they would work well at the higher voltage but, I guess, have a shorter lifetime.

I have been doing some research on sg setups in triode mode and it seems that the audio pentode and beam tetrodes were engineered to allow sg to be connected to plate at very high voltages. This is not the case for most transmitter valves where much lower plate voltages should be used when triode connected i.e. they should be run close to the sg maximum not the plate maximum... I have not found any data on line output valves yet. I wonder if this info is accurate though...

ciao

James
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Old 20th March 2003, 08:52 AM   #10
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Default Triode-strapped transmitting valves

Quote:
Originally posted by James D.


I have been doing some research on sg setups in triode mode and it seems that the audio pentode and beam tetrodes were engineered to allow sg to be connected to plate at very high voltages. This is not the case for most transmitter valves where much lower plate voltages should be used when triode connected i.e. they should be run close to the sg maximum not the plate maximum...
James,

Where does this information come from? The only maker's information that I have found is for 6146 (g2 max 250V) where Philips state that it can be run as a triode at 400V. 13E1 has a g2 limit of 300V and I have tested it flat out at 500V as a triode without problems.

Next week I have some transmitting valves coming. These are rated at 2kV anode and 400V g2. It is my intention to prepare triode curves for them since if they are linear as triodes I would like to run them at about 600V; this of course will require preparation of curves up to 1kV! Fireworks eh?

813 is more generous with its 1.1kV g2 limit; I expect that 1.5kV as a triode would be OK. I did consider this for a while, but these high voltages are no good for audio, since they mean enormous primary output loads, in the interests of getting a decent load line.

7N7
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