|
Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
|
Thread Tools |
12th Nov 2018, 5:19 pm | #1 |
Pentode
Join Date: Jan 2014
Location: Cape Town, South Africa
Posts: 214
|
Mystery Octal
Not the only no-name brand in my collection, but is it possible to ID this one from the pics?
|
12th Nov 2018, 5:49 pm | #2 |
Nonode
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
|
Re: Mystery Octal
That's a Mazda Octal valve. I can't tell what is the electrode structure or what is just a reflection in the glass.
|
12th Nov 2018, 6:24 pm | #3 |
Dekatron
Join Date: Jul 2008
Location: Charmouth, Dorset, UK.
Posts: 3,601
|
Re: Mystery Octal
Mazda octals have a wider space between the pins either side of the key but I don't recognise that as a Mazda valve. Looks a bit like an EL33.
Peter |
12th Nov 2018, 6:38 pm | #4 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
|
Re: Mystery Octal
NR77/EL35?
Lawrence. |
12th Nov 2018, 6:47 pm | #5 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
|
Re: Mystery Octal
It does look like an output pentode or beam tetrode, but the heater voltage could be anything.
|
12th Nov 2018, 6:51 pm | #6 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
|
Re: Mystery Octal
It does have something of the EL33/CL33 about it.
|
12th Nov 2018, 7:23 pm | #7 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
|
Re: Mystery Octal
Might be able to narrow it down by finding out as to whether or not the anode is of mesh construction.
Lawrence. |
12th Nov 2018, 10:07 pm | #8 |
Nonode
Join Date: Aug 2015
Location: Cambridge, Cambs. UK.
Posts: 2,196
|
Re: Mystery Octal
It looks like an EL37, that predecessor of the ubiquitous EL34.
Martin
__________________
BVWS Member |
13th Nov 2018, 8:22 pm | #10 |
Octode
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 1,205
|
Re: Mystery Octal
I also wonder whether it has a mesh anode.
If so it's probably an NR77 / EL35 / APW1295 like the one I have here, as Lawrence has also suggested. |
13th Nov 2018, 8:32 pm | #11 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
|
Re: Mystery Octal
Just another observation, the pics on the web appears to show that the EL35 and EL33 have a slight "waist" whereas the EL37 appears not to. The OP's photos seem to show a slight "waist"
Lawrence. |
14th Nov 2018, 2:15 am | #12 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
|
Re: Mystery Octal
I have got some photos of the EL37 for comparison.
They have different micas and round flat anodes and certainly not mesh anodes. The first photo is a pair with CV numbering in an amp that has now been restored and the second photo is a duff one showing that the anode indeed round. |
14th Nov 2018, 1:48 pm | #13 | ||
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
|
Re: Mystery Octal
Quote:
Quote:
If it IS a Mazda Octal, then that narrows choice down considerably of course! Maybe the OP can confirm. |
||
15th Nov 2018, 3:05 pm | #14 |
Pentode
Join Date: Jan 2014
Location: Cape Town, South Africa
Posts: 214
|
Re: Mystery Octal
Unfortunately there is not a single marking to hint at manufacturer or type. Looking at a close-up here: http://www.r-type.org/exhib/aaa1624.htm
it looks like an EL35. The main body of mine is blacked out so it's not possible to see the mesh anode mentioned. It has a curious little mesh near the base facing downward on a single arm. FWIW the reading between pins 2 and 7 is 2 Ohm. I'll try and post clearer pics. |
15th Nov 2018, 6:51 pm | #15 | |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,737
|
Re: Mystery Octal
Quote:
I could be wrong, but the 'curious little metal thing' sound like the 'getter', which is used during the latter part of the production of a valve to get rid of impurities inside the valve after the vacuum has been created. On many valves you'll see a mirror-like deposit on the inside of the glass close to the getter, deposited when the getter is 'flashed'. Sometimes the getter is a little ring like a halo at the top of the inside of the valve, which - when flashed - creates a mirror like deposit at the dome of the valve. When the valve has been flashed, the getter's work has been done, but it doesn't stop audiophools from thinking that one shape of getter is better than another and can improves 'tonal qualities' giving the valve an 'airy presence'. Using the term 'air' in the context of valves usually means the valve has gone down the gurgler. From Wiki: Quote: 8-< Flashed getter – The getter material is held inactive in a reservoir during assembly, then heated and evaporated after initial evacuation, usually by induction heating. The vaporized getter, usually a volatile metal, instantly reacts with any residual gas, then condenses on the cool walls of the tube in a thin coating, the getter spot or getter mirror, which continues to absorb gas. This is the most common type, used in low power vacuum tubes. 8-< https://en.wikipedia.org/wiki/Getter About 4 mins 15 secs into this video about hand-made high-end audio valves, you'll see a getter being inductively flashed: https://www.youtube.com/watch?v=DOR6Pn-tGPo Hope that's of interest.
__________________
David. BVWS Member. G-QRP Club member 1339. |
|
15th Nov 2018, 8:30 pm | #16 | |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
|
Re: Mystery Octal
Quote:
It's possible for a getter support to affect the performance of a valve, eg: microphony due to it being insufficiently supported. Lawrence. |
|
19th Nov 2018, 8:40 am | #17 |
Pentode
Join Date: Jan 2014
Location: Cape Town, South Africa
Posts: 214
|
Re: Mystery Octal
All very interesting! Glad I only have to plug valves in and not make them!
I have noticed the halo ring near the top in many wire pin valves, and the silver lining in close proximity. That explains the silver lining near the bottom of this valve close to the little grid as seen in the pic attached. As an aside, I recently used a dud valve and sprayed the top cap grey to give it an appearance of a working valve with a led light for effect on a Quad amp. Small things........... |
19th Nov 2018, 9:34 am | #18 |
Dekatron
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,273
|
Re: Mystery Octal
Have you tried the trick of breathing on the glass so that your breath condenses there. This can give a momentary view of faint lettering.
Try it on the top as well as the sides. Peter |
19th Nov 2018, 9:47 am | #19 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
|
Re: Mystery Octal
|
19th Nov 2018, 10:13 am | #20 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
|
Re: Mystery Octal
I have a number of these BRIMAR 6L6GA valves. They look very similar to the one illustrated. They may have an AMERTY connection dating from WW2.
John. |