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Author Topic: Pre-flight checkout  (Read 1943 times)

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Offline porcupunctis

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Pre-flight checkout
« on: June 09, 2015, 07:31:03 AM »
I purchased an Eros tube repro a few months ago and I'm just now getting my tape deck set up with a direct out.  I'm looking forward to putting this into my system and decided to run through the resistance and voltage checks to make sure everything shipped OK.

When I pulled the tubes to do the resistance check they were not what I expected.  In place of the 6922 was a Western Electric 396A which I understand to be similar to a 5670 like the ones in my Paramounts.

There were two very different tubes where the EF86s go.  The only number in common was X79.  One tube is additionally marked with 6X32 inside a large "C".  The other is marked 6H23n (actually the n looks more like the greek letter pi).  I can't find much on these numbers in the google world.

So, what I need to figure out is this: 
1. Has the unit been modified to work with these tubes?
2. Will it still work with the proper tubes?
3.  Could I be looking at an Eros rebuild in my near future?

Here is what I found doing a resistance check (switch toward output jacks)
Terminal strips 4, 12, 16, 17, 29, and 30 all should be 130K but are all consistently reading199K.
Terminal strips 6 and 7 should be at 470K but measure just under 20K
Terminal strip 27 should read 47K but only reads 21K

Randall Massey
Teacher of Mathematics
Lifetime audio-electronics junkie

Offline Paul Birkeland

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Re: Pre-flight checkout
« Reply #1 on: June 09, 2015, 07:39:46 AM »
In place of the 6922 was a Western Electric 396A which I understand to be similar to a 5670 like the ones in my Paramounts.
Yeah, that's no good. 
There were two very different tubes where the EF86s go.  The only number in common was X79.  One tube is additionally marked with 6X32 inside a large "C".  The other is marked 6H23n (actually the n looks more like the greek letter pi).  I can't find much on these numbers in the google world.
A 6J32P is a Russian EF86, so no issues there.

Do you have a 12BH7 in the 12BH7 socket?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Chris65

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Re: Pre-flight checkout
« Reply #2 on: June 09, 2015, 07:47:10 AM »
The other is marked 6H23n (actually the n looks more like the greek letter pi).

6H23p = Russian 6922

Offline Doc B.

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Re: Pre-flight checkout
« Reply #3 on: June 09, 2015, 08:45:42 AM »
It sounds like you need to go back to the seller and ask for some detail on the changes made. We're only going to be able to give SWAGs without a lot more info. The 5670 has an different pinout than the 6922 so the first thing you need to find out is if the amp was actually rewired to function with the 5670, or somebody who didn't know the difference just stuck one in the socket. That would be best sorted by comparing the circuit to the schematic, which is in the manual. Hopefully the seller included the manual with the preamp.
Dan "Doc B." Schmalle
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Bottlehead Corp.

Offline porcupunctis

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Re: Pre-flight checkout
« Reply #4 on: June 09, 2015, 09:05:59 AM »
OK, that helps.  I can concentrate on the wiring of that middle tube.  I have the manual so I can compare the build.

It was several months ago when I made the purchase.  As I recall, the seller wasn't the builder.

I tried looking through the Eros Tape forum to see if there was any talk of this particular build.  I did not find anything but maybe I didn't look deep enough.  The top plate was left natural and the base is finished in a piano black with a closed bottom.  A nice build overall. 
Randall Massey
Teacher of Mathematics
Lifetime audio-electronics junkie

Offline Doc B.

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Re: Pre-flight checkout
« Reply #5 on: June 09, 2015, 09:28:51 AM »
The easy way to tell if the socket has been rewired for the 5670 is that the heater supply wires will be connected to pins 1 and 9 rather than 4 and 5.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline porcupunctis

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Re: Pre-flight checkout
« Reply #6 on: June 09, 2015, 10:24:12 AM »
OK, heater wires are confirmed on pins 4 and 5.  So I'm going with the random tube theory.  Everything looks just like the picture in the manual.

I have a  pair of EF86 tubes on their way.  The others I have on hand.  I will wait to do the voltage checks when those come in.  That should time out well with me picking up the 1500 this weekend.

By Monday or Tuesday I could be 100% Bottlehead from the tape head out to the speakers.  Can't wait.
Randall Massey
Teacher of Mathematics
Lifetime audio-electronics junkie