Lafayette LR-800

[OutlawSun]

Well this is my first serious entry into tube gear not counting a Roberts reel-to-reel. It's a Lafayette LR-800 that has been recapped. Mostly runs great. Have a slight issue with it having a ringing hum when it's switched to FM stereo. It's faint in the background but noticeable. Seems to disappear if it's set to mono FM. Any idea what could be causing this?

 

[Tinkerbelle]

That's a clean looking receiver.

Not sure what ringing hum means as "ringing" and "hum" are generally used separately to describe different sound effects/conditions. It is not unusual for mono to come through more clear than stereo, especially for weak signals from what I have experienced. Ringing might imply some sort of oscillation vs, hum picking up noise, AC and such. A schematic of the tuning circuit might help.Otherwise, this might be something that someone familiar with tuners, alignments etc. will be better able to answer (Tuner forum) if you get no joy from here.

 

[OutlawSun]

That's a clean looking receiver.

Not sure what ringing hum means as "ringing" and "hum" are generally used separately to describe different sound effects/conditions. It is not unusual for mono to come through more clear than stereo, especially for weak signals from what I have experienced. Ringing might imply some sort of oscillation vs, hum picking up noise, AC and such. A schematic of the tuning circuit might help.Otherwise, this might be something that someone familiar with tuners, alignments etc. will be better able to answer (Tuner forum) if you get no joy from here.

I guess the best way to describe it is almost like a really low dial tone or test tone. Kind of a hard sound to describe. Will see if I can find the schematic and post it in a few.

 

[mhardy6647]

OP sez the weirdness is in FM stereo... ergo I'm guessing it's related to the MPX 'decoder'. I've certainly heard some weird things come out of mis-adjusted (or malfunctioning) outboard MPX adaptors; I reckon you have, too

 

[OutlawSun]

OP sez the weirdness is in FM stereo... ergo I'm guessing it's related to the MPX 'decoder'. I've certainly heard some weird things come out of mis-adjusted (or malfunctioning) outboard MPX adaptors; I reckon you have, too

Yeah only appears when set to FM stereo I half wondered if it was the stereo search tone somehow bleeding into the background even though it's supposed to be off. Wish I could find a copies of the manuals would be interesting to see explanations of stuff like the local and distant FM connections. Anyhow here's the schematic for it.

Edit: Here's a link to some better resolution copies.

http://audiokarma.org/forums/index.php?threads/lafayette-lr-800.479730/#post-6213107

 

[mhardy6647]

I am guessing it requires FM MPX alignment. Not for the faint of heart.
In fact, not for amateurs.

 

[peteCWA]

I just took a look at the service manual for the LR-800. In looking at the block diagram, I would suggest using a scope to trace out the various stages in the stereo/multiplex area. I would also test the tubes on a good tester to determine if any of them are acting flaky especially in this area. Since the majority of all the parts are 50 plus years old, this can a non-trivial trouble shooting activity. Re-cap is great if it was done correctly and without adding other problems.

 

[mhardy6647]

Free advice (and worth every penny ) be very careful fiddling about with tuned circuits. Everything matters in tuned circuits, especially higher frequency ones... changing a tube in the 'radio' part of the radio could require adjustments to the circuit's tuneable components, and changing even the passive components (e.g., capacitors) might alter the performance of a given circuit to point that the radio "functionality" is lost. Lead length, circuit layout and lead dress may be critical in parts of the circuitry.

Note that I have chosen my modal auxiliaries carefully and italicized them above . YMMV.
But, it's still prudent to be careful when digging into the radio part of a receiver, IMO/IME.

Just for fun here's a photo of the interesting side of a Fisher 400. The Fisher receivers are, I'd opine, very nicely laid out and well put together as well. I roughly circled the "radio" (FM only, in the case of the 400) parts of the receiver. Front end (tuner, RF amp and local oscillator on the left, IF strip sort of in the middle, and MPX stuff on the right.

 

[OutlawSun]

Free advice (and worth every penny ) be very careful fiddling about with tuned circuits. Everything matters in tuned circuits, especially higher frequency ones... changing a tube in the 'radio' part of the radio could require adjustments to the circuit's tuneable components, and changing even the passive components (e.g., capacitors) might alter the performance of a given circuit to point that the radio "functionality" is lost. Lead length, circuit layout and lead dress may be critical in parts of the circuitry.

Note that I have chosen my modal auxiliaries carefully and italicized them above . YMMV.
But, it's still prudent to be careful when digging into the radio part of a receiver, IMO/IME.

Just for fun here's a photo of the interesting side of a Fisher 400. The Fisher receivers are, I'd opine, very nicely laid out and well put together as well. I roughly circled the "radio" (FM only, in the case of the 400) parts of the receiver. Front end (tuner, RF amp and local oscillator on the left, IF strip sort of in the middle, and MPX stuff on the right.

View attachment 1258405

Oh yeah not messing with the tubes in the radio section without getting it professionally realigned in the process But it’s worth getting an idea of what could be the culprit. But yeah Fishers are works of art definitely plan to get one eventually. Figured this one would be fun to mess with in the meantime.

 

[mhardy6647]

Nothin' wrong with that Lafayette; Kenwood (TRIO) OEM... not junk by any stretch of the imagination.
And the one in this thread is a particularly pretty one. So many of hose old Kenwood receivers seemed to attract more than their share of incontinent rodents during prolonged storage, IME.

 

[OutlawSun]

Nothin' wrong with that Lafayette; Kenwood (TRIO) OEM... not junk by any stretch of the imagination.
And the one in this thread is a particularly pretty one. So many of hose old Kenwood receivers seemed to attract more than their share of incontinent rodents during prolonged storage, IME.

Definitely not knocking it. Knew these were essentially rebadged KW-70s. I plan to keep it for a long time. Wish I had the manual to get a better idea on the odd FM antenna connection arrangement on the back. Yeah this one came from the dry part of Washington so doesn’t seem like it’s seen rust. Other than some minor scuffs and a few faded letters it’s really clean. Been carefully dusting the chassis (mainly with q tips) and cleaned the dial glass as carefully as I could. It’s looking really good.

 

[OutlawSun]

I just took a look at the service manual for the LR-800. In looking at the block diagram, I would suggest using a scope to trace out the various stages in the stereo/multiplex area. I would also test the tubes on a good tester to determine if any of them are acting flaky especially in this area. Since the majority of all the parts are 50 plus years old, this can a non-trivial trouble shooting activity. Re-cap is great if it was done correctly and without adding other problems.

Don't suppose you could post some pics of that manual? I'm curious to see what if anything it says about the dimension adjustment in the chassis. Doesn't seem to appear on the Kenwoods.

 

[mhardy6647]

What's odd about the antenna connection? I think I see what looks like terminals for 300 ohm twinlead(?).

 

[mhardy6647]

You probably have this... but... in case you don't:


source: http://audiophool.com/Schem_A/LR-800-1.gif

Looks like unbalanced connection for the antenna? 75 ohm?

 

[Patrice B]

Yes, oscillation probably coming from a de-tuned 38Kc... or a bad cap/tube!

 

[OutlawSun]

You probably have this... but... in case you don't:

View attachment 1258969
source: http://audiophool.com/Schem_A/LR-800-1.gif

Looks like unbalanced connection for the antenna? 75 ohm?

There's three screws marked under FM a local, ground, and distant rather than the standard two and a single screw marked for AM. It's just a little unusual.

 

[mhardy6647]

As I say, looks to be unbalanced (if I am interpreting the schematic correctly) Strip back 75 ohm coax, hook center to "distant" (or "local" if you have very strong stations that might overload the front end) and run the braid to ground.

The weird part is just one AM connector -- I guess one is supposed to share the GROUND terminal if one has external AM and FM antennae?

It is odd that the LRE morph of this receiver has a different antenna input configuration than the TRIO/Kenwood morph.

 

[OutlawSun]

As I say, looks to be unbalanced (if I am interpreting the schematic correctly) Strip back 75 ohm coax, hook center to "distant" (or "local" if you have very strong stations that might overload the front end) and run the braid to ground.

The weird part is just one AM connector -- I guess one is supposed to share the GROUND terminal if one has external AM and FM antennae?

It is odd that the LRE morph of this receiver has a different antenna input configuration than the TRIO/Kenwood morph.

Yeah it's odd found a few different kenwood schematics from similarish models and there's nothing like it from what I saw. I honestly wish I had the operating manual just to see what the logic was in what they did with this. Here's photos of the connections front and back. In the image on the right the far right is the AM connection.

.

Bonus pic: Lafayette ad for the receiver. Figure it's handy to repost it for whoever in the future ends up with one of these and looking for info seeing as Lafayette catalog scans are pretty much impossible to find.

 

[mhardy6647]

ahem. That scan looks familiar

LRELA800 by Mark Hardy, on Flickr

 

[peteCWA]

Yeah it's odd found a few different kenwood schematics from similarish models and there's nothing like it from what I saw. I honestly wish I had the operating manual just to see what the logic was in what they did with this. Here's photos of the connections front and back. In the image on the right the far right is the AM connection.

. View attachment 1259272View attachment 1259273

From the operating manual:
"As indicated, there are three FM antenna screw terminals - LOC (Local), G (Ground) and DIST (Distant). In most cases, the 300 ohm twin lead from the antenna should be connected to the "G" and "DIST" terminals. This will generally ensure maximum receiver sensitivity and thus provide best reception of the weaker stations. If you are located in an area which is extremely close to stations, there is a possibility that the very strong signals will overload the receiver and cause distortion If this occurs, disconnect the wire connected to the "DIST" terminal and attach it to the "LOC" terminal. This reduces the sensitivity of the receiver and prevents overloading by too strong a signal."

"For AM reception in fringe areas or high noise areas, a random length of insulated wire can be connected to the terminal designated "AM""

For the FM antenna setup, a Local/Distant switch would have been more convenient but it would have impacted manufacturing cost.