The Other 13E1 SE-OTL

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Ray P
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#136 Re: The Other 13E1 SE-OTL

Post by Ray P »

Just ordered a couple of spare transistors so all being well the power-on will be next weekend.
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#137 Re: The Other 13E1 SE-OTL

Post by Ray P »

So this project has been sitting quietly on the shelf for the last six to eight months.

I'm on a bit of a roll having recently finished the Noir HPA, the DSD Decoder and now the 300B HPA with Soekris DAC so I'm picking this amplifier up again next. Tio do something a little different to Steve's 13E1 SE-OTL, I've decided to use the 6SN7 Aikido Cascade input/driver stage from the 6C33C SE-OTL project with the 13E1 output valves. This afternoon I've assembled and tested a Maida regulator for the Aikido stage B+ and a simple regulator for the 6SN7 filaments.

I would like to use regulated supplies for the 13E1s too but the cold resistance of the filament is about 2R7 so the initial current demand is close to 10A (filaments are nominally 26V @ 1.2A) and I don't thing a basic LT1085 type regulated supply is going to like that.
Last edited by Ray P on Tue Apr 21, 2020 10:38 pm, edited 1 time in total.
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pre65
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#138 Re: The Other 13E1 SE-OTL

Post by pre65 »

Is 26V @ 1.2A preferable to 13V @ 2.6A ?

Would the heater resistance centre tap (@26V) be preferable noise wise ?

I've got some LT1083 (7.5A) supplies made up if you need theory testing.
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#139 Re: The Other 13E1 SE-OTL

Post by izzy wizzy »

pre65 wrote: Tue Apr 21, 2020 10:34 pm Is 26V @ 1.2A preferable to 13V @ 2.6A ?

Would the heater resistance centre tap (@26V) be preferable noise wise ?

I've got some LT1083 (7.5A) supplies made up if you need theory testing.
Might come up against input voltage limits for those devices.
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#140 Re: The Other 13E1 SE-OTL

Post by Cressy Snr »

I found AC heating to be perfectly adequate. I used one 0-25V transformer winding per valve, with the heater centre tap pin at the valve socket taken to ground.
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Ray P
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#141 Re: The Other 13E1 SE-OTL

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Cressy Snr wrote: Wed Apr 22, 2020 10:05 am I found AC heating to be perfectly adequate. I used one 0-25V transformer winding per valve, with the heater centre tap pin at the valve socket taken to ground.
Yes, AC heating is what I'll go with. I was a little worried about consistently exceeding the filament rated voltage because of mains variation down here but I've got a lightly lower rated transformer and it seems OK now - I ran one of the 13E1 filaments early one morning when voltage seems highest.
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#142 Re: The Other 13E1 SE-OTL

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I've been drilling metal for a slightly reworked chassis this morning, hope to start assembling some of it this afternoon.
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#143 Re: The Other 13E1 SE-OTL

Post by Ray P »

I was having a bt of a tidy out last evening and found a pair of NOS RCA 12SN7GT valves I had forgotten about. I had planned to use 6SN7GTs for the input driver stage of the project.

As I have a 24VAC toroid for the 13E1 filaments it occurred to me that I could eliminate another transformer if I used the 12SN7GTs and connected their filaments in series. I would use a simple regulated supply powered from the 24VAC transformer (it has the current capacity), replacing an LM1085 with an LM317HV and uprating Cin to be safe with max Vin. Is there a downside to running DC filaments with two valves in series?

Or, maybe, just run the 12SN7GTs in series straight from the 24VAC transformer.
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#144 Re: The Other 13E1 SE-OTL

Post by Ray P »

Must be getting old! just realised that the filament transformer has two 0-12VAC secondaries, not a single 0-24VAC one, so essentially it's a 0-24V with a centre tap.

I'm no EE so this might be a really dumb question but I'll ask anyway; does that open the possibility of connecting a regulated supply across each 12VAC section (for the 12SN7 filaments) and still having the 24VAC across both secondaries for the 13E1 filaments? I ask because I already have two regulated supplies built and installed but I have nagging doubt...
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#145 Re: The Other 13E1 SE-OTL

Post by izzy wizzy »

Ray P wrote: Tue Apr 28, 2020 10:46 am Must be getting old! just realised that the filament transformer has two 0-12VAC secondaries, not a single 0-24VAC one, so essentially it's a 0-24V with a centre tap.

I'm no EE so this might be a really dumb question but I'll ask anyway; does that open the possibility of connecting a regulated supply across each 12VAC section (for the 12SN7 filaments) and still having the 24VAC across both secondaries for the 13E1 filaments? I ask because I already have two regulated supplies built and installed but I have nagging doubt...
You should get nearly 17V. Allow say 2V drop across the rectfiers using schottkies so 15V with a LDO reg you might just do it. But if then you connected the 13E1 filament to an audio ground, there will be a grounding or short issue as you then can't connect/ground the putput of the regs (thinking out loud). Without drawing it out, can't say for sure. Sounds overly complex just before lunch.

But what's wrong with AC on the SN7 heaters? One on one side, one on the other?
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#146 Re: The Other 13E1 SE-OTL

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izzy wizzy wrote: Tue Apr 28, 2020 1:06 pm You should get nearly 17V. Allow say 2V drop across the rectfiers using schottkies so 15V with a LDO reg you might just do it. But if then you connected the 13E1 filament to an audio ground, there will be a grounding or short issue as you then can't connect/ground the putput of the regs (thinking out loud). Without drawing it out, can't say for sure. Sounds overly complex just before lunch.

But what's wrong with AC on the SN7 heaters? One on one side, one on the other?
Thanks iw. I suspect the rating of the transformer will mean that I'll get over 18V, because my mains is always around 240V and it won't be fully loaded so regulation will leave it a little high, so I'm confident of getting 12.6VDC from a regulator running off one of the 12VAC secondaries. My nagging doubt is about the connections, with a regulator across each half of the centre-tapped secondary and a 13E1 filament across the full secondary. I'll do a quick diagram later.
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#147 Re: The Other 13E1 SE-OTL

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Here's a quick diagram - valid configuration?
Capture.JPG
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#148 Re: The Other 13E1 SE-OTL

Post by Nick »

Ray P wrote: Tue Apr 28, 2020 7:44 pm Here's a quick diagram - valid configuration?
Capture.JPG
As long as the heaters are all isolated then can't see why not.
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Ray P
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#149 Re: The Other 13E1 SE-OTL

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Nick wrote: Tue Apr 28, 2020 8:39 pm As long as the heaters are all isolated then can't see why not.
Thanks Nick, I've assumed all the heaters are not connected to ground (floating). When I get a moment I'll breadboard it and see how it goes.
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#150 Re: The Other 13E1 SE-OTL

Post by Ray P »

Yep, that worked! 120VA, 2 x 0-12VAC toroid, configured as above diagram, supplying two regulated supplies and two 13E1 filaments.

Rock steady 12.54VDC on the 12SN7GT filaments and 25.6VAC on the 13E1 filaments. That'll do.

Image
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