Osram 2v battery valve SE amp

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ACPEN
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#1 Osram 2v battery valve SE amp

Post by ACPEN »

Hello again!
It's 3 years since my last post, although I do check the site out fairly regularly and note that things appear quieter than before - due to people Iike me I dare say! Anyway, I hope all are well and still enjoying the hobby. I haven't been idle over the years but not done anything new. I've probably built most possible configurations but had always thought that one day I would build something using old 2v battery valves - they were what I started out with at the school radio club in the early '50's (yes, that old!) So here it is, basic SE using S24's HF tetrode (trioded) with VT-45 triode outputs nothing fancy except for (apologies) some 'sand' in between' (under the EF54 cans) I always do this now as it has proved reliable and makes adjusting bias very easy. The S24's are battery biased (in line).
Anyone else tried similar? I remember some 4v Osram amps a while back.
Sound is amazingly clean! The use of the VT45's is not their intended purpose but being rated at 3.5W with ht limit of 300v its somewhat unusual for a battery valve! (440mA Filament)
Picture attached (I hope...)
Regards
David.
20210215_121231-4.jpeg
simon
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#2 Re: Osram 2v battery valve SE amp

Post by simon »

Proper valve amp! :-)
Cressy Snr
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#3 Re: Osram 2v battery valve SE amp

Post by Cressy Snr »

That is totally cool 8)
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Ray P
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#4 Re: Osram 2v battery valve SE amp

Post by Ray P »

Image
Sorry, I couldn't resist!
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Thermionic Idler
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#5 Re: Osram 2v battery valve SE amp

Post by Thermionic Idler »

OK, I HAVE to know where that numbered knob came from, I want one for the front panel of my linestage!

That's a lovely looking thing.
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pre65
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#6 Re: Osram 2v battery valve SE amp

Post by pre65 »

Thermionic Idler wrote: Wed Feb 17, 2021 3:28 pm OK, I HAVE to know where that numbered knob came from, I want one for the front panel of my linestage!

That's a lovely looking thing.
Agreed. :)
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ACPEN
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#7 Re: Osram 2v battery valve SE amp

Post by ACPEN »

Audiojumble Tonbridge many years ago - always worth a visit, but when?
David. :D
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Ray P
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#8 Re: Osram 2v battery valve SE amp

Post by Ray P »

Thermionic Idler wrote: Wed Feb 17, 2021 3:28 pm OK, I HAVE to know where that numbered knob came from, I want one for the front panel of my linestage!

That's a lovely looking thing.
Guitar stores?

https://www.thomann.de/gb/control_knobs.html?ls=25
Sorry, I couldn't resist!
ACPEN
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#9 Re: Osram 2v battery valve SE amp

Post by ACPEN »

Following on from the above, I searched for any original use of the HF tetrode (S23) in legacy radio's of the pre war period - I found a service sheet for a Philips radio (1935) in which an equivalent (PM12a) was used, unusually as an audio amp. The interesting thing is that it appears to be used within the reverse resistance (slope) area with anode at 53v and screen at 35v - I can tell you that it works well! But how? Normally any use of such valves at audio stipulate that this area of negative resistance is avoided at all costs with anode at around 100v and screen at 70v (ish) otherwise severe distortion sets in (yes it does!)
Anyone been here before or thoughts on what's going on...

Reds
David.
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Dave the bass
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#10 Re: Osram 2v battery valve SE amp

Post by Dave the bass »

Question from the kid at the back of the classroom...

The 'reverse slope', is that referring to the 'kink' in the anode curves of a tetrode?
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#11 Re: Osram 2v battery valve SE amp

Post by ACPEN »

Hi Dave - pleased to hear from you, and yes, correct!
All you need to now is explain whats going on....

😁
David.
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Mike H
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#12 Re: Osram 2v battery valve SE amp

Post by Mike H »

Hello ACPEN, nice to see you still around. Cracking looking amp alright. I'm trying to do something similar, now got a wooden box, it's not an old one tho.
 
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Dave the bass
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#13 Re: Osram 2v battery valve SE amp

Post by Dave the bass »

ACPEN wrote: Tue Mar 09, 2021 3:14 pm Hi Dave - pleased to hear from you, and yes, correct!
All you need to now is explain whats going on....

😁
David.
Good to here from you too David.

If I knew what was going on....erm.... I'd ...erm.... know whats going on!
"The fat bourgeois and his doppelganger"
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