The "Not OTL" 13E1 Build

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Cressy Snr
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#1 The "Not OTL" 13E1 Build

Post by Cressy Snr »

OK so now the breadboard for the 13E1 OTL has been recycled into a circuit with output transformers, namely the relatively inexpensive Hammond 1627SE.

The object of this exercise was to forcibly stop the breadboard development of the OTL, otherwise I would have just carried on with the OTL breadboard ad infinitum and then run up against Owston with nothing to show but a dangerous rats' nest.

Now this is never going to be as good as the OTL, as OTLs, particularly those of the single tube variety, seem to have a way with music, that to my ears is unsurpassed by anything else I've heard.

Another objective was to try out a 13E1 amp with the 6H30pi twin triode as an input/driver stage and here it is:
Image

Very nice it is too in terms of overall presentation. The 6H30pi is very linear and even better, it maintains that excellent linearity at low plate voltages. Each section is running at less than 60V on its plates, from a 110V supply.
As we can see, these 13E1s are the 1950s STC ones with only the anode supports as cooling fins. I wouldn't want to be using these in a single tube OTL; it would be too unkind to them.
Last edited by Cressy Snr on Wed Jan 16, 2019 12:36 pm, edited 2 times in total.
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RhythMick
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#2 Re: The "Not OTL" 13E1 Build

Post by RhythMick »

Very nice. Watching...
Cressy Snr
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#3 Re: The "Not OTL" 13E1 Build

Post by Cressy Snr »

The 1627SE are configured for 16 Ohms to give a 1.25K load for the 13E1 when an 8 Ohm speaker is connected.
If I'd never heard a single tube OTL with this valve, I could quite easily live with this. The 6H30pi is an excellent match in terms of synergy, for the 13E1, which does bode well for the OTL build.
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Ray P
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#4 Re: The "Not OTL" 13E1 Build

Post by Ray P »

Great stuff Steve.

Just looking to order some octal 6H30pi valves; I had forgotten how hungry the filaments are so l may need a bigger transformer too!
Sorry, I couldn't resist!
RhythMick
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#5 Re: The "Not OTL" 13E1 Build

Post by RhythMick »

I think I have some 6H30pi. Let me know if you have trouble sourcing, though I think they are plentiful yes? Still made?
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Ray P
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#6 Re: The "Not OTL" 13E1 Build

Post by Ray P »

RhythMick wrote: Wed Jan 16, 2019 5:44 pm I think I have some 6H30pi. Let me know if you have trouble sourcing, though I think they are plentiful yes? Still made?
Cheers. the B9 version are easy to get hold but the octal version, which I need for my chassis are less common but obtainable. I think EH still make them. Apart fron the envelope the two versions are, I believe, identical.
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#7 Re: The "Not OTL" 13E1 Build

Post by Cressy Snr »

Yep, they are still made; at least the nine pin noval base valve is. Mine are the gold plated pin version by New Sensor, under the Electro-Harmonix brand.

The "Alexandra Palace" amplifier may yet rise again; except this time it'll actually have enough gain! :mrgreen:
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RhythMick
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#8 Re: The "Not OTL" 13E1 Build

Post by RhythMick »

I'm pretty sure I have a pair of EH octal 6H30pi. Let me know if you want me to hunt through my boxes.
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Ray P
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#9 Re: The "Not OTL" 13E1 Build

Post by Ray P »

RhythMick wrote: Wed Jan 16, 2019 8:35 pm I'm pretty sure I have a pair of EH octal 6H30pi. Let me know if you want me to hunt through my boxes.
If you have pair that you don't need I'll be interested in taking them off your hands. PM me with what you want for them if you can locate them. Cheers
Sorry, I couldn't resist!
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#10 Re: The "Not OTL" 13E1 Build

Post by RhythMick »

Ray P wrote: Wed Jan 16, 2019 9:58 pm
RhythMick wrote: Wed Jan 16, 2019 8:35 pm I'm pretty sure I have a pair of EH octal 6H30pi. Let me know if you want me to hunt through my boxes.
If you have pair that you don't need I'll be interested in taking them off your hands. PM me with what you want for them if you can locate them. Cheers
I'll take a look. No idea what they're worth, except I know I bought them from new and haven't used them. Of course I might not find them, I'm not the most organised of people.
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Ray P
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#11 Re: The "Not OTL" 13E1 Build

Post by Ray P »

RhythMick wrote: Wed Jan 16, 2019 10:26 pm I'll take a look. No idea what they're worth, except I know I bought them from new and haven't used them. Of course I might not find them, I'm not the most organised of people.
OK lets see if you find them and take it frm there
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#12 Re: The "Not OTL" 13E1 Build

Post by Cressy Snr »

I've had an interesting couple of days with this amplifier.
The Hammond 1627SE 2K5 output transformers sound considerably less 'thick' with the whole of the secondary winding in use and series connected end to end as it has to be with 13E1s, which need a 1.25K reflected primary load. The transformers are remarkably good configured like that. I did try running the 13E1 into a 2K5 load, and as expected the power dropped off and things thickened up, so the 1K25 load is better, both in terms of output power and sound.

The 1640SEA Hammonds are 1.25K and will take 200mA DC bias current, more in line with the capabilities of the 13E1, but would they, apart from allowing a higher output power sound any better? Who knows and I'm not paying to find out. :)

As it stands, the 13E1 amp is putting out around 3WPC into my 8 Ohm Fanes, which is perfectly adequate for 98dB efficient speakers and about the same as my pink SET did. The output valves are running at 113mA, with a 120V a-k voltage. The 1627SE transformers will take 130mA, so there is reasonable headroom built in to the output arrangements. Running like this, these 1950s 13E1 ought to have a long life.
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steve s
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#13 Re: The "Not OTL" 13E1 Build

Post by steve s »

That's a really low impedance valve
It should have a good damping factor too.. good work Steve...
I sort of wish I had kept mine now..
But in have the da100s to mess with but I don't think I'll be risking them in an otl...
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#14 Re: The "Not OTL" 13E1 Build

Post by Cressy Snr »

steve s wrote: Fri Jan 18, 2019 6:01 pm That's a really low impedance valve
It should have a good damping factor too.. good work Steve...
I sort of wish I had kept mine now..
I'm glad you didn't but I can understand how you might feel. When I built the Alexandra Palace thing ten years ago I didn't really know how to keep the 13E1 under control, so never realised the potential they had to sound so great.

As I said right at the start of the OTL thread, the valves were lying completely forgotten about in my box of rectifiers and regulators, then Ray started talking about the 6C33C, which somehow caused one of those lightbulb moments to happen.
....I have the da100s to mess with but I don't think I'll be risking them in an otl...
I should ruddy well hope not! :lol:
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#15 Re: The "Not OTL" 13E1 Build

Post by Cressy Snr »

A bit of tweakery to the output transformer equipped breadboard over the weekend.
An independent power supply for the front end and driver stage has been installed in the top left corner of the board, just below the DC heater supply:
Image
Funnily enough, this has made an improvement to the noise and sound performance, whereas on the OTL the opposite was true; go figure.

At the bottom of the pic is the output stage CLC power supply, made up of two 80uF Eyuda oil filled motor run caps and a Danbury 10H choke. The tall, black, caps, just above the PSU are 800uF JJ electrolytic cathode bypass caps, across the 150R outout stage cathode resistors.
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