Hypothetical Attempt at V76M boards

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Potato Cakes

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Winston O'Boogie said:
P.S.  This is right up PRR's alley, he can do this stuff while also filling out everyone else's tax returns.

I'm less of a "doing all the maths beforehand" guy as that stuff was never my strong suit.
I'm quicker just lashing it up and adjusting stuff until it fits.
If I get stuck then that's when I take a time out and do all the sums.

There are other dudes on here who excel at that stuff though so, hopefully someone comes along to offer a hand.

:)

I usually have to resort to strapping everything together then figure why it didn't work as I don't have a reference of the various formulas needed and when they are applicable.

I think the best solution to move forward with getting an actual board laid out is to leave a spot for a resistor or an off board inductor as those would be sizable enough to make sense to keep it off the PCB. This is ultimately a DIY project so there will be room for additions and substitutes per the builder's taste and imagination.

Also, following further review I think it would be better to keep these as single channel boards with an off board PSU. This will make this circuit accessible to more people who may only want a single channel.

I still have some reading to do regardless...

Thanks!

Paul
 

Winston OBoogie

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shabtek said:
wonder if PRR has just been busy moderating the IRS forum...

:D Yeah.  I have seen him posting on DIYAudio recently so it seems he's doing OK which is good to know.

Paul, I think your idea of placeholders for resistor or off board inductors is good.

I always include the variables in a first board run myself - better/easier chance of it working without having to hack it.  Jumpers or omitting a component is easier than cutting traces.

You can always do revisions on a 2nd run if needed.  I bet there'd be enough folks who'd take any initial boards left over from a 1st run so you can cover your cost.  As long as it's got pads for options/getting out of jail etc.   

Like you say, this is DIY

:)

 

Potato Cakes

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Winston O'Boogie said:
:D Yeah.  I have seen him posting on DIYAudio recently so it seems he's doing OK which is good to know.

Paul, I think your idea of placeholders for resistor or off board inductors is good.

I always include the variables in a first board run myself - better/easier chance of it working without having to hack it.  Jumpers or omitting a component is easier than cutting traces.

You can always do revisions on a 2nd run if needed.  I bet there'd be enough folks who'd take any initial boards left over from a 1st run so you can cover your cost.  As long as it's got pads for options/getting out of jail etc.   

Like you say, this is DIY

:)

Just a show of hands, how many people would be interested in something like this? If I can cover costs then I would be more motivated to get this done sooner.

I'm going to contact the guy that has been doing PCB design for me in the past and start working on an estimate of initial expenses.

Quick tangent, will running the tubes with 12VDC heaters cause a significant shortening of the tube's life or performance? I'm trying to sort out the PSU requirements and the spec sheets for EF804 and 83S rate their current draw based off of 6.3V but there isn't a range of nominal voltages for the filament. If increasing the voltage will have less draw on the PSU then I would prefer going that route if the penalty for doing so is negligible. I don't want to derail myself with another topic and if the short answer is "don't do it" then I'll leave it at 6.3V and press onward.

Thanks!

Paul
 

Potato Cakes

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I heard back from Lundahl regarding chokes and they said they do not to custom windings as they do not offer inductors with values that high. I am still waiting to hear back from Cinemag.

Thanks!

Paul
 

Potato Cakes

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Lundahl sent a follow up email and it seems that their 1667 will do 250H and 400H at the current draw amounts per the schematic. Sowter said to expect a 12 week lead time for their 1377 and 1378 chokes but possibly sooner as they are taking on more staff.

No word from Cinemag yet.

Thanks!

Paul
 

Winston OBoogie

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The Lundahl Ll1668/5mA and Ll1668/10mA  have 500H+ and 200H+ at the DC and signal currents used in the V76.

The Ll1667 has more inductance at the same currents, but also more dcr and capacitance.

The 1667 type is probably closer to the original BV514 and BV515 in terms of sloppiness of anode DC due to the dcr but, generally, if the inductance is high enough for the low end, then LL1668 is a better anode choke.

I guess Ll1667 is a safer bet as far as inductance for low end, but Ll1668 has better high end due to the lower capacitance, hence me saying the 1668 if inductance is high enough. 


 

Winston OBoogie

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Thought about this last night, did a few load lines, some reading up, maths etc and -  I believe both of the valves in the V76 that are choke loaded are basically acting more or less like triodes that have a CCS in the anode.  Strapping both valves as triodes and putting some solid-state stuff above them should get them acting like they are with the inductors.
A resistor would get you a bit of the way there, fed from a clean 350V H.T. supply, still with the valves strapped as triodes.  But those inductors help linearize the 2 valves and also raise the gain close to the triode'ed mu of the valve.  It'd be a bit sloppy with just resistors.

Needs an active load also fed from that same 350V B+  .  Tube or solid state active ccs, either would work

Edit:  Or -  Make each stage out of cascoded pairs and plot the load lines individually for top and bottom.  Then apply ultra-linear feedback to convert to mostly triode.  The E83F isn't quite all triode but that 2nd EF804S is about spot on. 

Can't get through all the maths to figure out what the supply might need to be then, but gut tells me it'd probably have to be higher still...  like 470V DC.  Ouch!

Anyway... 


Edit
 

Potato Cakes

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Winston O'Boogie said:
Thought about this last night, did a few load lines, some reading up, maths etc and -  I believe both of the valves in the V76 that are choke loaded are basically acting more or less like triodes that have a CCS in the anode.  Strapping both valves as triodes and putting some solid-state stuff above them should get them acting like they are with the inductors.
A resistor would get you a bit of the way there, fed from a clean 350V H.T. supply, still with the valves strapped as triodes.  But those inductors help linearize the 2 valves and also raise the gain close to the triode'ed mu of the valve.  It'd be a bit sloppy with just resistors.

Needs an active load also fed from that same 350V B+  .  Tube or solid state active ccs, either would work

Edit:  Or -  Make each stage out of cascoded pairs and plot the load lines individually for top and bottom.  Then apply ultra-linear feedback to convert to mostly triode.  The E83F isn't quite all triode but that 2nd EF804S is about spot on. 

Can't get through all the maths to figure out what the supply might need to be then, but gut tells me it'd probably have to be higher still...  like 470V DC.  Ouch!

Anyway... 


Edit

470VDC is definitely quite high. For myself I think I'm going to stick with inductors at this point. The pricing I got from the US distributor for Lundahl is very reasonable. I still would be interested in exploring the use of plate resistors but maybe that could be a followup thread after I hopefully get some boards made sooner than later.

I'm working on a rough layout that I'll post later this week.

Thanks!

Paul
 

Winston OBoogie

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Yep. 

All the other, non inductor methods of doing/trying this are possibly worth trying, academically speaking.  They each might be better, worse, identical... 

But they're not the same circuit as a V76, for better or worse. 

Lundahl is good stuff and not expensive for what it is.
The US dealer is a cool guy too, Kevin.
 

Winston OBoogie

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Still mulling this over and, I believe the 2nd valve with the inductor (the EF804S) is running  'almost' triode but is operating (I think) as mu X 2 (about 40) so, the plate impedance is higher than triode, but not crazy high.
I'm confident the Lundahl LL1668/5mA would be fine there. 

On the E83F, I'm having a hard time computing the anode Z (brain freeze) but, again, I think the Lundahl LL1668/10mA will be fine in that spot.

With any inductor (especially these low dcr Lundahl's) you'll need to adjust the screen grid resistor for the usual 1/6th or so of SG current.  This because the lower dcr of the Lundahls will drop far less B+ so, get your screen grid at the voltages shown :  170V for the EFF804, and 130 for the E83F. 


On your earlier post, running the heaters at 12V6 is fine.  Whatever is easy.

Do you need a simple regulator for the main H.T.?  I could draw a schem of what's worked for me.  Or not, you can plow your own furrow

8)
 

jensenmann

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A friend started winding replacement inductors for V76s some month ago. We measured some of his coils a few weeks ago and they seem to be spot on within specs. I´ll invite him to pass by in this thread as he´s a member her, but not posting much. Maybe he can contribute a bit.
 

MrDude

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HI There Guys!

My Friend Jens gave me the info for this thread.

I Rewind and manufacture 100% New Drop in replacements for V76 and V72 Chokes.
These were tested in a original V76.

See pictures:



I Also have a Working 5-CHamber prototype, tested in the original units.





Making the BV515 is also possible, allthough I'd maybe use a bigger M core and not a EI core.

If you are interested you can mail me:

info@audiosohn.com

Or PM me.

I am also thinking of setting up a store in the white market maybe?
If interest is big enough.

Best,

Felix

 

Winston OBoogie

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MrDude said:
HI There Guys!

My Friend Jens gave me the info for this thread.

I Rewind and manufacture 100% New Drop in replacements for V76 and V72 Chokes.
These were tested in a original V76.
 

Woo Hoo! 
Hi Felix, that's great.
Thanks for coming on here and letting us know.
I don't know what the rules are for selling and White Market etc.  but if you have enough products to sustain paying for the add in there, then sure, do it.

Otherwise, I don't see the harm in just figuring a way to just get your chokes into the hands of folks on here who want them.

Tell us what they cost for V72 and the BV514 & BV515 for the V76.

I'm personally interested in the V72 just as much as the V76 chokes so...

Cheers :) 

P.S.  They look great by the way, that multi 3 & 5 chamber is what's missing from the other offerings from Lundahl, Sowter, Cinemag etc. 

Sent you a PM.
 

Potato Cakes

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MrDude said:
HI There Guys!

My Friend Jens gave me the info for this thread.

I Rewind and manufacture 100% New Drop in replacements for V76 and V72 Chokes.
These were tested in a original V76.

Great news indeed, Felix. I will be emailing you soon.

Thanks!

Paul
 

Winston OBoogie

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Wanted to put in a good word for Felix.

I messaged him on Friday about a couple of V72 inductors.  After a quick chat I sent him the dosh,
which was a good price for what's involved. 

Anyway, he emailed me Sunday lunchtime  (2 days later) to let me know they're done!

Obviously I don't have them yet, but from what I see, and what he talked about, they seem spot on.
I can't wait  :)
Thanks Felix
 

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Winston OBoogie

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I received the chokes from Felix.  Beautiful job.  Reminds me of the type of work done by a watchmaker or a maker of precision parts for a Leica camera.

I haven't been able to test them yet, but I did have a friend unsolder and measure original chokes in two V72S modules which came from a REDD.17 desk.

From these rough measurements, Felix's work is spot on.  I don't expect any surprises when I use them

One point which I was a little uncertain on but Felix set me straight is:  hook up the wire that's the end of the winding on the last coil to your anode for the lowest capacitance.
In my case that's the blue wire to anode.  Black wire to H.T./B+

Over & out. 
 

Potato Cakes

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Winston O'Boogie said:
I received the chokes from Felix.  Beautiful job.  Reminds me of the type of work done by a watchmaker or a maker of precision parts for a Leica camera.

I haven't been able to test them yet, but I did have a friend unsolder and measure original chokes in two V72S modules which came from a REDD.17 desk.

From these rough measurements, Felix's work is spot on.  I don't expect any surprises when I use them

One point which I was a little uncertain on but Felix set me straight is:  hook up the wire that's the end of the winding on the last coil to your anode for the lowest capacitance.
In my case that's the blue wire to anode.  Black wire to H.T./B+

Over & out.

Great news, Winston.

I will be ordering some of these when I get closer to completing the board layout. Are you going to use them for the Bv515 position as well? I was told by Felix he was only doing Bv514 currently as the 515 was a bit more effort but you had mentioned earlier that it one might could make the decision to just use the same value for each position. It might be less accurate but it would/could still sound amazing.

Thanks!

Paul
 

Winston OBoogie

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Potato Cakes said:
Great news, Winston.

I will be ordering some of these when I get closer to completing the board layout. Are you going to use them for the Bv515 position as well? I was told by Felix he was only doing Bv514 currently as the 515 was a bit more effort but you had mentioned earlier that it one might could make the decision to just use the same value for each position. It might be less accurate but it would/could still sound amazing.

Heya Paul.
Bummer  about Felix not feeling comfortable winding the BV515, I was actually waiting on V76 chokes and hoping he'd do that one too.

The V72 choke will certainly work in place of the BV514 but I think Felix's actual BV514 would be better there and probably no more expensive.

Unfortunately, neither the BV514, nor the V72 choke will work very well in place of the BV515 as they'd both saturate in that position,  the BV514 more so than the V72. 
We have about 3mA on the anode where the BV514 is in the V76, about 6mA in the V72, but about 11mA on the anode of the E83F in the V76.

To use the same choke for both we'd need to err on the side of a BV515 type.  While this would work, it would likely have a bit more capacitance when used in lieu of the BV514 so, use Felix's BV514 there.

For a BV515 we could:  1/ persuade Felix to do it, or  2/ use the Lundahl I suggested earlier in that position.

The Lundahl 1668/10mA will work well there I'm sure and the only thing I'd include is a spot on the pcb to add an additional dropping resistor (maybe around 9K - 10K if your B+ is 280V, but adjust on test until the anode voltage is 170V) and a small bypass cap (10uF).  Both of these parts after the main B+ feed, right before the Lundahl.
The screen grid feed would stay as is, ie. not via this extra dropping resistor, but directly from the B+ line.
 
This is because the Lundahl has far les dcr than the original BV515 and will drop much less voltage at the 11mA on the E83F anode.

So to sum up, use Felix's BV514 and Lundahl 11668/10mA

Make sense?

P.S.  I got the V72 chokes to build this obscure EMI amplifier based on the V72 but using 6BR7 valves. 
I don't plan on it being a clone as I'm using them in parallel triode and cascoded instead of pentode.
This is to lower the noise etc. 

It might just end up a useless rat's nest so my backup plan for these chokes is a regular V72S or V77 type  :D

 
 

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