US made "Shell" high fidelity amplifier - Info?

I've variac'ed life back in this little amp. It's playing but not sounding very good, yet!

When I first put the tubes back in and turned it slowly up it didn't play at all. A little hum and only one of the output 7189 tubes was glowing. Actually only three out of six tubes glowed and got hot.

Some shots of De-oxit in the the tube sockets (amp turned off) help and now 5 out of six are glowing and the amp is playing. I can't get the last 12ax7 to light up and have tried swapping the 2 12ax7s around, even tried with other 12ax7s. This little 12ax7 will not glow!

I guess that is why the amp doesn't sound good yet, there is lots of distortion, especially if I turn up the bass.

Edit: I forgot to mention that the two last tubes are 12au7s. How the amp is designed is not clear to me (I'm still not technical skilled!).


Peter Q
 
I'm giving the little Shell amp another try and fired it up to night. I still doesn't sound good. Distortion from both channels.

What is most likely; the 7189 tubes are worn down or some other component has failed after some 40 years?

I wonder if I could give it a try with some (not important) el84 tubes -just for a short while to test the amp without the 7189s? Or maybe I should get a pair of Russian 7189 (el84Ls) like these on ebay?

PQR
 
Leaky capacitors are likely, weak tubes are a possibility. Caps are cheap, and seem most likely - they'd affect EVERYTHING.
 
Tom Bavis said:
Leaky capacitors are likely, weak tubes are a possibility. Caps are cheap, and seem most likely - they'd affect EVERYTHING.
Click to expand...

Thx Tom,

Changing the capacitors most be the way to go.

Here is the layout of the below of the amp:

shell-10.jpg


I find two not identical paper "Super-cap. dry electrolytic capacitors":


shell-12.jpg


with the value of 10 mfd and 450 V DC
and:

shell-13.jpg


with the value of 100 mfd and 50 V DC.

Knowing next to nothing about electronics the amp being a two channel amp I expected to find two of everything (almost). But it does not seem to be symmetrical constructed. I guess it is not a SE amp with two 7189 tubes but some kind of PP with a double use of each tube?

At the AV 100 V outlet I find a new (newer) Danish cap (0.5 mfd, 600 WV AC/400 WV DC) between the chassis and one of the legs of the poles of the outlet; similar cap - but apparently original - is at the other poles of the outlet.

shell-14.jpg


Bonus info: i've been feeding the amp via a small variac and a 220V/110 V stepdown transformer. I've noticed that the amp sounds a little bit better (a little less distorted) when I kind of overfeed it (about 120-125 V I guess) with the variac. What does that show?

Peter Q
 
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The caps from line to chassis are called "Death caps" by the guitar guys... you don't want any leakage there! The 0.5 uF does NOT belong - it will pass about 25 mA at 120V/ 50 Hz and that could be deadly. The amp will work without either one - I remove them and change to a 3-wire cord. The disc caps are probably OK, the electrolytics are probably bad. The big silver can cap MIGHT still be OK, but if it heats up, it's bad for sure.
 
Tom Bavis said:
The caps from line to chassis are called "Death caps" by the guitar guys... you don't want any leakage there! The 0.5 uF does NOT belong - it will pass about 25 mA at 120V/ 50 Hz and that could be deadly. The amp will work without either one - I remove them and change to a 3-wire cord. The disc caps are probably OK, the electrolytics are probably bad. The big silver can cap MIGHT still be OK, but if it heats up, it's bad for sure.
Click to expand...

Thx again,

The original "Death cap" seems to be 0.033 mfd while the replaced are 0.05 mdf (not O.5 mdf as I wrongly wrote).

Guess I have to replace the two electrolytic caps? The big silver cap must be part of the power supply: since it's not hot, not leaking and the amp is not humming I guess it is OK.

Bye the 3-cord do you mean that I should make add a ground wire connected to the chassis instead of the two death caps?

Do you have any clues about the layout of the amp Singled ended or not?

Peter Q.
 
pqrannes said:
My geography knowledge of New York State isn't good enough; was the company itself situated at Long Island?

PQR
Click to expand...

Yep! FWIW, Harmon Kardon was 1st located in Plainview LI, not to far from Westbury.

To think, Growing up on LI, I was surrounded by all this great gear!
 
The little Shell tube amp - alive and kickin'

I owe it to you to follow up on this story.

I did change the two yellow caps to new ones and it didn't change a bit. The little amp still sounded distorted and so.

Then recently I borrowed a good and calibrated tube tester (AVO 160) and among the many tubes I tested were the two 7189 from the Shell. The two tubes actually tested very bad (down to about 20-30% on the AVO).

From Berlin, Germany, I ordered at pair of Sovtek el84M which are substitutes for the 7189s. The tubes arrived before X-mas and along with other tested (and good testing) tubes the Shell was re-tubed.

Does it play? Yes, indeed! How does it sound?

I first tried it out (on the bench) with a pair of uneven vintage speakers in no-name (and open) boxes. It sounded very good and promising. I then (still on the bench) tried it out with a pair of full range Coral Beta 8 in a pair of Lowter Acoustica 116 back loaded horns: I must admit I found the sound a bit boring and unpersonal.

Then back from x-mas days at the summer cottage it set the Shell amp properly up with a pair of 60s German Isophon PH2132 full range speakers units in big open boxes (the rear side is removed) like this:

ikea-ben%20010.jpg

(this is not my music room)

And this set-up sounds very, very good. I'm amazed!

The sound stage and image in the "hotspot" are better than I have ever heard it here before. Sitting in the right position the music forms a 3D circle round you head and you are 'in the middle' of the music ....... (this is goose bumps!)

Normally I play on a huge pair of three-way horn speakers (very much like Klipsch Belles) and a Braun CSV-13 el84 PP tube amp or a SS Sansui AU-9900 with eg. Dynaco A-25 (or JBL L-86s or something else). But I've never been near a sound stage and image like this with my many set-ups previously.

And it got me thinking. Is it the little SE tube amp or the (kind of) open baffle full range speakers that are doing the trick? Or maybe the combination?

Peter Q.
 
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Well, while you good people overcome the season (and Christmas) celebration (Happy New Year to everyone) and (especially) add at bit of info about the rare Long Island-based Shell Electronics, I got curious and made a little test.

I ran the open-baffle-ish speaker with my Braun CVS-13 el84 pp tube amp. And the conclusion? The magic in the above mentioned setup is the little SE-7189 tube amp! The Braun sounded OK with OB-ish Isophon but the magic was gone.

Thus: the magic comes from the unknown Shell Northport SE tube amp!

What I still need to find out is this: are SE tube amps known to have very goog imaging and sound stage? Or is this little amp just very good?

Next test to run is to try the amp out with my Klipsch Belle-ish three way speakers. But not to day, the first day of another year, one test a day is enough. Now I'll turn to music (an album by Mark Hollis of "Talk Talk").

Peter Q.
 
I don't know about SE & soundstage, but most of the tube amps I own are single-ended. Been experimenting with SE & push-pull amps for close to 5 years now. Harmonics, less feedback, more direct signal path, who knows, they just sound better to me. Glad you got yours working like you want, is it time to update your sig? :)
 
Nirky said:
... is it time to update your sig? :)
Click to expand...

I guess it is. I've got a lot of stuff and changes happen all the time. Maybe I should keep the signature less specific?

Thx for you feed back!

PS I've just edited my sig!
 
More Shell Electronic amps

A friend just spotted two Shell tube amps in two ebay auctions.

Here they are:

http://cgi.ebay.com/Shell-Stereo-60s-vintage-tube-Stereo-Int egrated-Amp_W0QQitemZ250472664888QQcmdZViewItemQQptZVintage_ Electronics_R2?hash=item3a51558f38&_trksid=p3286.c0.m14

http://cgi.ebay.com/TUBE-SINGLE-END...s_R2?hash=item53dc1fe8eb&_trksid=p3286.c0.m14

And for future reference (when the auctions are all gone) here are some pictures.

The little SE (a near sibling to mine):

se-4.jpg


and the other larger model 2020P:

shellstereo-1.jpg


If only they weren't for sale on the wrong side of the Atlantic ...

PQR
 
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Your post will probably be edited since links to auctions are not allowed outside D&S... cool little amps though...
 
What's that object between the "Treble" and "Bass" knobs?

Is that a power indicator lamp?

Also, can you post a pic of the underside?


KGB
 
KGBMAN said:
What's that object between the "Treble" and "Bass" knobs?

Is that a power indicator lamp?

Also, can you post a pic of the underside?

KGB
Click to expand...

Which amp are you referring to?

I don't have other pictures than the ones in the auctions (which are not mine).

Pictures of the underside of my amp are to be found earlier in this thread.

PQR
 
That's a tuning eye tube.. no idea why it's on that piece though, because there isn't a tuner that I see of... interesting.. maybe using it as a power level indicator?
 
Cute little amp. I've got one almost exactly like it. Mine was labeled "XAM Mark IIIb", or something like that. I think it was sold in the EJ Korvette stores way back when. I gutted the nasty tone circuit out of mine, and added in a volume knob. It's a perfectly serviceable amp. One of these days I'm going to strip it down completely and rebuild it into an RH84. I've also seen the same amp under the "American Fidelity" name, except it didn't have the vacuum tube rectifier. They converted the supply to solid state diodes at that point.

 
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