KLH Model 21 found at Goodwill today!
 

Hello everyone today I found at Goodwill (work) a KLH Model 21 on the shelf in the electronics section in the store its kind of in rough shape as its missing the bass control knob and the grille cloth is coming loose and its got some lavander colored paint splatters on it but I figure for $7.99 one couldn't go wrong with such a classic piece of electronics history. So anyways I would like to know a little more about this unit as far as when it was made and a little bit about how it works and also as to where I could get a replacement knob for the bass control and how I could go about cleaning up the paint spatters on the unit. Any help and information would be appreciated.

Thanks,

Levi

Pictures are posted below.

I Google-searched it and found 7,840 results. Including one on Shopgoodwill com that sold for $60. You got a nice employee discount!

Thanks, and yeah I thought so too. I plugged it in to try it out and it seemed to be just a 60 hz. hum coming out of the speaker and no reception on the tuner so I'm guessing that the filter capacitor needs to be replaced at least, which is a 2000 MFD 30V electrolytic capacitor. As for the grille cloth it looks like it should be fairly easy to repair it. When I opened it up it looked like i was the first one to ever open the unit up as it still had its sound dampening pillow inside the case yet and it was pretty clean inside hardly a spec of dust inside the unit.

I have used a product called "goof off" successfully to remove latex paint splatters without damaging the underlying wood finish on older radios... I suspect that it would work ok on the KLH.

jt

Alright, I'll see about picking up a bottle of that. The only problem is that there's some paint spatters on one of the knobs as well and I tried scratching it off with my fingernail and it wouldn't come off and I know goof-off isn't going to be good to use on something like plastic because it has stuff in it that hard on plastic, so I wonder what I would use on the knobs to clean them up.

Try the new Goof Off 2. "SAFE ON PLASTIC!"

http://ecx.images-amazon.com/images/...L._SL1500_.jpg

OK, I'll see if I can find some.

Well I replaced the original 2000 MFD 30V Power Supply Cap in the radio with a 2200MFD 50V capacitor and its still has a 60Hz Hum coming out of the speaker and still no audio out of the speaker from the tuner. So what should I check next in the circuit that could be causing my issue? I also tried posting this in AudioKarma but for some reason when I went to post it it wouldn't post it would act like it was going to post the thread but then it would wouldn't actually post anything.

I would suspect that one or both of the diodes in the rectifier circuit could be shorted or have very high reverse leakage... you can get a manual here from Phil's old radio site:

http://antiqueradio.org/KLHModelTwentyOne21FMRadio.htm

Thanks again to Phil Nelson for his wonderful site,
jr

KLH built some very nice stuff. Our shop saw a lot
of it being 20 miles from Cambridge. Also piles of
H.H. Scott that was 5 miles away.
Anyhows change ALL the lytics first. I remember a few
of the stereo ones going DEAD in one channel & that
was it. ( 30 yrs ago ). Another thing that may be it
is if it uses ua703 IC's in the IF they were trouble
especially on Scotts sets. In any case when its running
again you will wonder what all the hoopla about digital is.

73 Zeno:smoke:

Thanks for the link, I tried to download the service manual but the link to the service manual in Phil's Website didn't work. :sigh:

Try the link again. Perhaps the download is a bit slow, but it works fine here.

http://antiqueradio.org/art/KLH21ServiceManual.pdf

.

I believe mine's an original 21 so I don't think it has any IC chips in it. The electrolytics don't appear to be bad but of course they could be bad even if they don't look it (no cap bulge). The electrolytics are mainly on the amplifier board, there aren't any on the tuner board surprisingly enough. Now I noticed that the Model 21 has an RCA Plug that says "Tuner out" was this meant to be able to have a multiplex unit hooked up to it so it could be FM Stereo like the Model 8? Also I'm missing one of the knobs on this unit and I was wondering where I might source a replacement knob for this unit.

It would download but nothing would show up as far as pictures or images go, it was just a blank grey page.

It's a 27-page PDF file. Must be some trouble on your end.

.

The link works for me. Might want to try right clicking and choosing 'Save Link as'. Takes forever for my browser to open the PDF if I simply open the link.

Link akso works fine for me... but here is another resource from AK:

http://akdatabase.org/AKview/display...album=35&pos=0

jr

Yeah it will let me navigate through the pages but the printed pages themselves aren't showing up in the PDF Download. So I'm not sure what's going on.
So I figured out that it must of been my Adobe Reader plugin on my web browser that was screwing things up because when I downloaded the file onto my computer and then opened it with Adobe Reader on my Computer it worked fine.

The ua703, if made by Fairchild, looks like a slightly larger transistor. The brown button ones were extremely unreliable. IIRC, they were replaced by a GE-IC12, NLA.

So What's the modern substitute for this part? Is there an NTE Part that subs out for this part?

http://ecx.images-amazon.com/images/I/41E0d5ilH1L.jpg

Some members here may still have some epoxy ones in their parts bins, but you may have to substitute one of these metal ones:

http://www.amazon.com/IC-AMP-8-LEAD-...productDetails

http://ecx.images-amazon.com/images/I/31GwKn1xmJL.jpg

.

Am I missing something here? I don't see any ics in the schematic for the set... just 11 transistors :scratch2:

jr

There are multiple version and revisions of the Twenty-One.

From the looks of his, it's probably one of the early (non-IC) versions.

Pictures of the boards inside his unit could confirm this.

.

Interesting! thanks for the info... guess we need some chassis pix.

jr

Here's some pictures of the insides of the unit.

First picture is of the tuner board, second picture is of the IF board, third picture is of the amplifier board.

Since the IF board is shielded, I can't see if the active devices are transistors or ics.

But first things first, regardless of the type of device used for IF amplification, IMHO, the hum problem needs to be resolved before further problems can be addressed.

jr

Well if the filter capacitor wasn't the cause of the hum (it still hummed even after the filter capacitor was replaced) what else could cause the radio to have a 60 Hz hum?

Post 9 jr tech mentioned the rectifiers. My thought too. You checked both of those?

My first guess was on post 9 (bad power supply diodes), but there are additional filter caps on the audio board to check/ replace. Shorted output transistors could also place a hogh load on the power supply and cause hum.
Does the volume control change the loudness of the hum or is it always there?

jr

Is the hum still there when the volume is all the way down?

.

Yes the hum is there no matter what the volume level is at even when the volume is turned completely down. and like I said whatever is causing the hum noise is also I'm sure causing the unresponsive tuner issue as well.

No I didn't check the diodes yet, that was the next thing I was going to check, would I check them with the diode function on my DMM? Also when I go to check the diodes do I need to remove them from the circuit to check them or can they be in circuit yet to check them? Also would a couple 1N4007 diodes work in place of the original diodes if they do turn out to be bad?

Edit: I checked the diodes and here are my results:

Diode 1:
171
118 in reverse

Diode 2:
174
119 in reverse

I measured the diodes with the radio unplugged and turned off, I'm not sure what the numbers mean but maybe some of you guys on here might be able to interpret the results for me as to whether or not my measurements mean the diodes are good or bad, or whether or not I need to have the radio plugged in and powered on to test more accurately, also the diodes were tested using the diode function on my DMM.

Likely you will need to unsolder one end of each diode to get a good test... should read "OL" in one direction and something around 300 to 700 mv in the other direction (depending on the type of diode).

jr

They are of the "top hat" variety of diodes it says on the diode case 1N2859 on both. They're soldered in rather precariously so I may just cut one of the leads and if they test fine I can just solder them back into place.

Well I cut one side of each diode out of the circuit and they measured around 600mV for both of them one way and measured "OL" going the other way which means they are working as they should be apparently which means that there must be something else causeing the humming and unresponsive tuner issue besides the diodes.

Sounds similar to this one: http://audiokarma.org/forums/index.p...mmmmmm.525449/

.

On IC's it may not have used them. They went disco in the
80's IIRC. The way the IF is built I would NOT go
there unless needed.

If the main filter is not the hum check the outputs next
& any transistors direct coupled to them. They will probably get HOT fast.
Its probably the transistors mounted on the chassis in round
holders.

73 Zeno:smoke:

According to a thread on AudioKarma where a guy had a unit that had the same exact issue as mine (where it hummed and no audio minus the blown fuse issue because mine hasn't blown its fuse yet surprisingly enough) they said something about the amplifier's coupling caps being bad which then in turn caused the output transistors to become fried like bacon, and once he replaced the coupling caps on the amplifier board and replaced the output transistors it worked fine for him. I'm hoping that's not what happened with mine because the amplifier board is going to be darn near impossible to remove because for some reason or another the amplifier board's mounting screws are covered in solder so there's no way to unscrew them... :sigh:

Well I guess I can forget about working on the tuner board specifically on the vernier tuner mechanism because the screws wont budge and the heads keep wanting to strip out on me whenever I try to remove them, which tells me they used poor quality aluminum screws for that part for some reason, which is odd because the rest of the screws they used were stainless steel screws...

I'm guessing that the screws that attach the amp board to the heat sink might be filled in with solder to prevent removal... these *should* be left intact. the screws that hold the board/heatsink assembly to the chassis are the ones that need to be removed to remove the amplifier.
Try a better screwdriver on the tuner screws. Do you have any "Liquid Wrench" ?

jr

No I don't have any liquid wrench, and I tried all the screwdrivers I have on the screws and they won't budge without just about stripping out the heads. So I don't know what to say about those screws. although those screws do have a very bad case of cadmium disease as well as a lot of other parts in this unit.