please help identify jennen tube amp.

mrneedle · 23rd June 2012, 08:07 PM

hi everyone,

finally bought a tube amp, going to pick it up next wednesday. but i was curious if someone could tell me more about this amp.

the seller tolled me it's a "TYPE : stereo NS40"

i can see a couple of 12ax7's but that's about it.

looking at the inside photo it reminds me of a bocama la-224b, but i could be mistaken there...

tried searching for a schematic but could find any information about this amp...

so i really could uses some help finding it, before i can go and restore this beauty to it's former glory.

TheGimp · 23rd June 2012, 09:15 PM

It looks like four 6BQ5s, a 12AX7, Front right can is 12AX7, rectifier is highly likely to be a GZ34, and the getter looks about shot.

I would not power it up in that shape. It needs rework before applying power.

HollowState · 23rd June 2012, 09:22 PM

This unit looks like pretty standard stuff from around the mid sixties. Looking at the pictures I can see two pairs of 6BQ5s in push pull full pentode mode with cathode bias. There is a 6BL8 pentode/triode which should be the phase splitter (concertina) and voltage amplifier (one each channel). A 12AX7, and probably two more under the shields, for phono and tape head preamplifier duties. Reminiscent of similar units from Scott, Heathkit, Lafayette and others.

HollowState · 09:53 PM

Quote:

Originally Posted by TheGimp

... rectifier is highly likely to be a GZ34, and the getter looks about shot.

I agree on the 5AR4 but remember from an earlier thread, these older ones last a long time even with a receding getter.

rotaspec · 23rd June 2012, 09:32 PM

I don't know anything about the particular amp, but the tube line-up is more or less conventional.
Output pairs are EL84 (6BQ5), phase splitters are ECF80 (6BL8), and the rest look to be ECC83 (12AX7).
The choice of ECF80 is interesting, but I have built a nice sounding EL84 PP amp using those as phase splitters. Those tubes are cheap and plentiful as they were used in TVs and oscilloscopes commonly.
It looks to be a nice easy restore job if the iron is OK (before switch on, my first check would be continuity of the output transformer primaries, and safety of the mains earth connection).

Hope that helps some.

Gary

mctavish · 24th June 2012, 11:50 AM

Its a Japanese amp that's been re-branded, outputs are probably quite good quality. Worth restoring IMHO.

kevinkr · 24th June 2012, 03:56 PM

Yes, it looks Japanese to me too.. And quite well made.. It appears that it might have been designed to operate on 110 (117V) based on markings on the rear panel so double check before plugging in. (Do not plug in before servicing!) Hopefully since you are in Holland, and it's a Dutch brand it is actually a 220V model.

JJ and FT make electrolytic caps that should adapt easily to this design.. Note that there are a lot of paper caps in this thing that will be bad from long experience - all must be replaced.

mrneedle · 24th June 2012, 05:56 PM

Thanks everyone for this very usefull information

My uncle agreed to help me with this project (he is an electrician) but i will keep you posted on my progress and probbably will have some more questions for you later on

mrneedle · 18th January 2013, 08:12 PM

sorry to resurrect this but, as you may have noticed some other projects came along first..

now i finally decided to strip this amp and cannibalize it for parts.

and have removed the OPT, and measured them... i assumed them to be about 8k into 8Ω, but my calculations say to me it is 4k into 8Ω.......

i applied 7.08v AC then secondary gives 0.453v

so
7 / 0.453 = 15,5
15,5 * 15,5 = 240,25
240,25 * 8 = 1922
1922 * 2 = 3844
=3.8k @ 8Ω

is this possible for a push pull el84 amp??

23rd June 2012, 09:22 PM	#3
HollowState diyAudio Member Join Date: Aug 2006 Location: Taxland, New Jersey	This unit looks like pretty standard stuff from around the mid sixties. Looking at the pictures I can see two pairs of 6BQ5s in push pull full pentode mode with cathode bias. There is a 6BL8 pentode/triode which should be the phase splitter (concertina) and voltage amplifier (one each channel). A 12AX7, and probably two more under the shields, for phono and tape head preamplifier duties. Reminiscent of similar units from Scott, Heathkit, Lafayette and others. __________________ "The supercomputer is technologically impossible. It would take all of the water that flows over Niagara Falls to cool the heat generated by the number of vacuum tubes required." ~ Professor of Electrical Engineering, New York University

24th June 2012, 03:56 PM	#7
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Yes, it looks Japanese to me too.. And quite well made.. It appears that it might have been designed to operate on 110 (117V) based on markings on the rear panel so double check before plugging in. (Do not plug in before servicing!) Hopefully since you are in Holland, and it's a Dutch brand it is actually a 220V model. JJ and FT make electrolytic caps that should adapt easily to this design.. Note that there are a lot of paper caps in this thing that will be bad from long experience - all must be replaced. __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

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23rd June 2012, 09:15 PM	#2
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	It looks like four 6BQ5s, a 12AX7, Front right can is 12AX7, rectifier is highly likely to be a GZ34, and the getter looks about shot. I would not power it up in that shape. It needs rework before applying power.

23rd June 2012, 09:32 PM	#5
rotaspec diyAudio Member Join Date: Nov 2007	I don't know anything about the particular amp, but the tube line-up is more or less conventional. Output pairs are EL84 (6BQ5), phase splitters are ECF80 (6BL8), and the rest look to be ECC83 (12AX7). The choice of ECF80 is interesting, but I have built a nice sounding EL84 PP amp using those as phase splitters. Those tubes are cheap and plentiful as they were used in TVs and oscilloscopes commonly. It looks to be a nice easy restore job if the iron is OK (before switch on, my first check would be continuity of the output transformer primaries, and safety of the mains earth connection). Hope that helps some. Gary

24th June 2012, 11:50 AM	#6
mctavish diyAudio Member Join Date: Feb 2008 Location: Niederösterreich	Its a Japanese amp that's been re-branded, outputs are probably quite good quality. Worth restoring IMHO.

24th June 2012, 05:56 PM	#8
mrneedle diyAudio Member Join Date: Nov 2011	Thanks everyone for this very usefull information My uncle agreed to help me with this project (he is an electrician) but i will keep you posted on my progress and probbably will have some more questions for you later on

18th January 2013, 08:12 PM	#9
mrneedle diyAudio Member Join Date: Nov 2011	sorry to resurrect this but, as you may have noticed some other projects came along first.. now i finally decided to strip this amp and cannibalize it for parts. and have removed the OPT, and measured them... i assumed them to be about 8k into 8Ω, but my calculations say to me it is 4k into 8Ω....... i applied 7.08v AC then secondary gives 0.453v so 7 / 0.453 = 15,5 15,5 * 15,5 = 240,25 240,25 * 8 = 1922 1922 * 2 = 3844 =3.8k @ 8Ω is this possible for a push pull el84 amp??