help on id of tubes

woodturner-fran · 13th March 2006, 10:38 PM

Hi all,

I recently bought an audio innovations 300 amp:

http://www.drtube.com/img/icon-gif.gif

The amp is push-pull 10W with phono stage thats switchable between MM and MC.

7 tubes in this thing, 4 ECL86, 2 ecc83 (12AX7) plus one other that has absolutely no markings on it. It looks like a 12AX7, but the internal structure at the bottom of the tube looks a bit different to the other 2 12AX7s .... could this just be maunfacturing differences? The tube is the same size and shape as the 12AX7 with the same number of pins.

Theres so little about this amp out there, that I though I might ask here first about the mystery tube!

Many thanks in advacne for any help that anyone can give,
Fran

EC8010 · 13th March 2006, 10:54 PM

Perhaps if your link worked, it would be possible to comment...

Turbo7MN · 14th March 2006, 01:12 AM

The 6EU7 is basically a 12AX7 with a different pinout. Do pins 1 and 2 look like they are for the heater?

Is this the schematic you were trying to link to?

http://www.drtube.com/schematics/ai/ai300mk2.gif

woodturner-fran · 14th March 2006, 11:09 AM

Hi,

yes. thats the schematic... sorry for the link not working in the post above..

How would I check if pins 1 and 2 are for the heater? (I'm only new at this!)

Fran

woodturner-fran · 14th March 2006, 03:31 PM

Hi all again!

OK, I've thought about this for a bit longer and have wondered about coming at it from the other side. If i pulled the unmarked tube from the socket, what tests can I do to tell what it is? Can I measure resistances and so on across certain pins?

Fran

EC8010 · 14th March 2006, 03:44 PM

Quote:

Originally posted by woodturner-fran
Can I measure resistances and so on across certain pins?

No. A far better method would be to look into the valve and identify which pins are which. The anode is the big outer structure, the heaters are the white wires coming out of the centre. The cathode is the (often cylindrical) sleeve surrounding the heaters, and the grid surrounds the cathode. When you know the pin-out it becomes easier to trace the circuit around the unknown valve. The component values and working voltage will give a clue as to what the valve is.

Frankly, in an amplifier of that era, it's likely to be an ECC83/12AX7.

kevinkr · 14th March 2006, 04:53 PM

Is that schematic similar to your model amplifier? If so the type may be an ECC82/12AU7 which from memory was a type audio innovations did use.

woodturner-fran · 14th March 2006, 09:05 PM

Yep,

as far as I can tell thats the schematic.... However, if you look at the schematic there are 4 ecl 86 - OK, I understand that the schematic shown uses "half" and ecl86 and that only one channel is shown. Then there is the ecc 82 - this is for one channel and there would be another ecc82 for the other (in mine these are the ecc83) - this would be the preamp section. What isn't shown in that schematic is the 7th tube that I have and must really be for the phono stage?

Another clue is that the ecl86 are mullard, which means they were replaced at one time, but the ecc83s are "precisa" - which were the tubes supplied originally in this amp, but the last mystery tube has no label so must have been replaced at one stage.

Will take a few photos and post them here, maybe that would give a better idea.

Can I just say thanks for all your efforts so far!

Fran

woodturner-fran · 14th March 2006, 09:17 PM

Guys,

I just got the info!!!!!!

the tube complement is:

4XECL86 (6GW8)

2xECC83 (12AX7)

1XECC82 (12AU7)

Many many thanks for all your help..... hope the info helps someone else at some stage.

Fran

13th March 2006, 10:38 PM	#1
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	help on id of tubes Hi all, I recently bought an audio innovations 300 amp: http://www.drtube.com/img/icon-gif.gif The amp is push-pull 10W with phono stage thats switchable between MM and MC. 7 tubes in this thing, 4 ECL86, 2 ecc83 (12AX7) plus one other that has absolutely no markings on it. It looks like a 12AX7, but the internal structure at the bottom of the tube looks a bit different to the other 2 12AX7s .... could this just be maunfacturing differences? The tube is the same size and shape as the 12AX7 with the same number of pins. Theres so little about this amp out there, that I though I might ask here first about the mystery tube! Many thanks in advacne for any help that anyone can give, Fran

13th March 2006, 10:54 PM	#2
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Perhaps if your link worked, it would be possible to comment... __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

14th March 2006, 04:53 PM	#7
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Is that schematic similar to your model amplifier? If so the type may be an ECC82/12AU7 which from memory was a type audio innovations did use. __________________ www.kta-hifi.net

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14th March 2006, 01:12 AM	#3
Turbo7MN diyAudio Member Join Date: Feb 2006 Location: East central MN	The 6EU7 is basically a 12AX7 with a different pinout. Do pins 1 and 2 look like they are for the heater? Is this the schematic you were trying to link to? http://www.drtube.com/schematics/ai/ai300mk2.gif

14th March 2006, 11:09 AM	#4
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	Hi, yes. thats the schematic... sorry for the link not working in the post above.. How would I check if pins 1 and 2 are for the heater? (I'm only new at this!) Fran

14th March 2006, 03:31 PM	#5
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	Hi all again! OK, I've thought about this for a bit longer and have wondered about coming at it from the other side. If i pulled the unmarked tube from the socket, what tests can I do to tell what it is? Can I measure resistances and so on across certain pins? Fran

14th March 2006, 09:05 PM	#8
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	Yep, as far as I can tell thats the schematic.... However, if you look at the schematic there are 4 ecl 86 - OK, I understand that the schematic shown uses "half" and ecl86 and that only one channel is shown. Then there is the ecc 82 - this is for one channel and there would be another ecc82 for the other (in mine these are the ecc83) - this would be the preamp section. What isn't shown in that schematic is the 7th tube that I have and must really be for the phono stage? Another clue is that the ecl86 are mullard, which means they were replaced at one time, but the ecc83s are "precisa" - which were the tubes supplied originally in this amp, but the last mystery tube has no label so must have been replaced at one stage. Will take a few photos and post them here, maybe that would give a better idea. Can I just say thanks for all your efforts so far! Fran

14th March 2006, 09:17 PM	#9
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	Guys, I just got the info!!!!!! the tube complement is: 4XECL86 (6GW8) 2xECC83 (12AX7) 1XECC82 (12AU7) Many many thanks for all your help..... hope the info helps someone else at some stage. Fran

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