Idiot check/ help with daft tube idea

[mondogenerator]

I have a couple of V1505 triodes and wonder what I'm getting into....

The datasheet is here

http://www.r-type.org/pdfs/v1505.pdf

I was hoping that I could run at very reduced voltages (for this monster tube) for easier PSU design. Say 400VDC as a limit...give or take.

Looking up in datasheet curves with an anode voltage of 400V to get looking in the linear (ish) region requires a Vg of manageable size but anode current of 1.5 amps!

Am I reading the graph plot correctly???

I figure I'd have to drive it with something usually reserved for output stages like EL34 6L6 KT88 but my question for the experts is

Is building a modestly rated amplifier (100W perhaps) running greatly reduced plate voltage practical?

I realise the heater power alone is around 50W but I choose to ignore it...

 

[nigelwright7557]

The heater power supply will be expensive.
I would put them on ebay and with the funds build a quad El34 output amplifier.

 

[pcan]

My short answer to your second question is no.

- huge amount of heat to remove. Fan probably needed.
- insanely expensive custom output transformers.
- oversize chassis, very heavy.
- shortened tube life due to low anode power dissipation / atypical working point
- no guarantee that the end result will sound nice.

 

[PRR]

....requires a Vg of manageable size but anode current of 1.5 amps!...

And 1.5A at near 400V leads to near 300 Watts, above your goal and likely your budget.

BUT the real choker is that reaching 1.5A Ip 160V Vp requires 0.4 Amps of Grid current!

This is not "driver stages for KT88" but an actual set of KT88 (at least) as drivers to pass this huge current into the V1505 grids. (And a pair KT88 will meet your 100W goal without the V1505s' help.)

More to your goal: 400V supply can hit 100V and 0.75A peak which makes 112 Watts. Plate load per side is 300V/0.75A or 400 Ohms, so 1,600r plate to plate. Peak grid current is 0.2A at 80V, which is 16 peak Watts at 400 Ohms. So still looking at a *power* amplifier to drive the V1505 grids. And no tubes really want to drive 400 Ohms directly. Also note that at 50V peak the equivalent load is nearer 700 Ohms, tending to infinity for very small signals. Driver distortion into highly nonlinear grids is likely a tougher problem than the V1505s.

Pair of triode-wired 6L6/EL34, any happy p-p circuit. Get a 25W transformer 6K primary, 600r CT secondary driving the V1505 grids. The CT goes to a stiff bias voltage, adjustable up to +12VDC at 0.1 Amps. Trim this for least driver distortion: you want the impedance of both grids small-signal to approximate the impedance of one grid at peak power.

All of this plus your heap of heater power is a fairly complex and silly build. Especially for mono (you just have the two V1505?).

 

[mondogenerator]

This is why I don't usually drink...

Thanks PRR and all....

I figured this was mere drunk inspiration (I.e. idiot check confirms my presence hehe)

I I have a bunch of BVA EF37, Brimar ECC88 and Mullard ECF80 that I've seen 'some' schematics for....

I have around 6 V1505 sat around. A couple obviously leaky and no good (white deposits inside envelope) but I suspect at least a pair are unused NOS kept as spares for decades and probably function.

I guess they could be sold but I'm not sure anyone would want them?

Was considering making a pair of table lamps seeing as the filament is so substantial! Even that is less simple than expected given the heater power!

Thanks (I must remember not to drink and DIYA)

 

[Tubelab_com]

This is not "driver stages for KT88"

I would look at something more practical for the driver, say a 6SN7......and a big freakin mosfet!

No this is not a practical amp, but it would be different. Would it sound good?????

The highish Mu would result is a low damping factor without some feedback. On the positive side the OPT could probably be a mains toroid, and no negative voltages are required.

To me the hard question is "can you get sockets for these things?"

 

[huggygood]

SE Output Transformer x2 Tube Valve Triode GM-70 4212 V1505 845 Rohrenverstarker | eBay

8/

 

[HollowState]

To me the hard question is "can you get sockets for these things?"

Probably not. But if you can purchase a used Eimac SK500 socket assembly you can make one from it's parts. The collet style connectors are 3/8 inch just like the tube pins. Remount them in the correct pattern on a suitable insulating material like ¼ phoenlic or G10 fiberglass. Be certain to leave wiggle room like the original socket to assure an easy fit and prevent breaking the tube. This will work for other big tubes as well like a 212E.

 

[6A3sUMMER]

If you like the looks of that tube, then get four 212E tubes (try and find those, let alone good ones).
Then build a pair of Push Pull monsters.
You will find the 212E amps much more practical.