On 5 Mar, 20:39, "hr(bob) " wrote:
On Mar 5, 1:44 pm, wrote:



On 5 Mar, 19:14, "hr(bob) " wrote:

On Mar 5, 11:19 am, wrote:

On 5 Mar, 15:10, wrote:

On 5 Mar, 02:18, "hr(bob) " wrote:

On Mar 4, 5:18 pm, wrote:

I have a very old valve radio from a company called Lafayette.
It has 6 valves which are
6v6 gt
6x5 gt
6sq7 gt
6sk7 gt
6sa7 gt

This radio was working fine but recently has developed the following
problem, when the volume is increased the sound is distorted
completely,
it can only be heared ok when the volume is very low, and putting the
ear onto the speaker. Any ideas?

Sorry, I accidently posted it to the wrong group.
To add to the above, it is a MW/LW/SW type
and the problem occurs on all of the bands.

Thanks in advance.

Got a model number? It sounds like a transformer powered all-band
1940's superheterodyne set. Later sets used 12, 35 and 50 Volt
versions of those tubes in series diretly across the AC power mains.
Then they were replaced by miniature versions of the same type of
tubes. The schematics for these sets are all almost identical, the
6say is converter, 6sk7 is IF amp, 6sq7 is detector and 1st audio amp,
and 6v6 is audio output, 6x5 is rectifier. Volume control is at input
to 1st audio amp. Do you have a scope so you can look at the signal
from that point to the speaker? If so, I can walk you thru the testing
needed.

H. R. (Bob) Hofmann

Bob, thank you. I don't have a scope.
I think you are right about the "series" thing. They are protecting
the valves these way, if someone takes one out everything stops
working.

Here is more information:

The model number is very faint, but it ends with E629, maybe IE629

There is also a 4 digits serial number, 2xxx
Probably not too many of those about today :-)
Made in America
Rated 110 to 125 Volts 50-60 cycles 40W
Yet (strangely) was always operated from 220V.

I need to change the power cable, it is probably the original and
is crumbling in a very dangerous way, so I might get a glimps
to the internal components. It looks like a big job simply to take
the unit out from the wooden box without damaging the tuning
mechanics. I wonder if it can simply slide out or if it needs to
be lifted out (bad).

Oh, and another interesting thing, the pickup coil doesn't use
ferite core like nowadays, there is a huge drum and on it the
coil is wrapped.

I have just finished replacing the power cable. The unit came out as
a whole, which was easy. I then was able to see all the
components inside. It is very messy as in those days they were
no printed circuit boards, but the general impression I got was
that damaged was caused to the internal part/s due to storage
in the attick, and last summer here in England the summer was
the hottest on record, so you can imagine... Everything looks
shining, a sort of wet-look, this must mean bad news.

On the positive side, I did manage to fix one of the two front panel
illumination bulbs - it seemed to be just a contact issue, and after
whasing the bulb in some water, it was working again. Now remains
only the audio problem.

I have taken some pictures, I will post them soon.

If someone wants this radio, make me an offer. I can ship
worldwide, and I accept paypal.

Thanks.- Hide quoted text -

- Show quoted text -

When you plugged the radio in after replacing the pilot light for the
front panel, were the lamps the same brightness as before the line
cord was replaced. If so, then the line cord must not have been used
to drop the line voltage from 230V to 115V. The set must be using a
power transformer designed for an input of 230V and not the 115V shown
on the back panel that you mentioned. I will see what info I can
find. Do you have a high-empedance voltmeter available to check the
votages on the tubes? Is the bottom of the radio accesible? Do you
know how to count tube pins from the keyway?

Bob Hofmann

Hello Bob,
(and others)

I am not sure about the brightness, since I received you message
after I had done the work, I didn't pay much attention to this.
I do have a digital DMM. Here are some pictures that I took
while repairing the power cord:

http://www.geocities.com/lafayettera...internet.com/- Hide quoted text -

- Show quoted text -

I went to "nostalgiaair.com to see if the model number worked. I
couldn't find anything close, perhaps you can go to the site and see
if anything rings a bell.

Ok, with a digital multimeter, we should be able to get going. Let's
assume that the radio did not get fried due to a doubling of the input
voltage. We will check the B+ voltage for some sanity, and then go
from there. There should be a large chassis-mounted electrolytic
capacitor rated 30 uf or larger, at 200V or higher. The can should be
grounded to the chassis, and there should be two non-grounded lugs
connected to various components.

Check the DC voltage on each of the two lugs. I would expect each of
the voltages to be at least 150V DC, maybe as high as 350V, one should
be a few volts higher than the other. Is the speaker a permanenet
magnet speaker, or is the place where the magnet normally is located
actually a coil of wire with two wires leading to it (in addition to
the 2 wires that go to the speaker cone)?

Bob, can please explain were do I measure, from the pin of the
canned capacitor to where? If both pins of the capacitor are
almost at the same level, why is it a 200V rating?

I will check the speaker for you. It is mounted on a transformer, I
need
to get another picture for you. BTW, John has noticed one capacitor
with Italian markings, and I noticed that the canned capacitor has
Russian writing. This may suggest the originals were replaced. If so,
this could be a recurring problem.


If you don't see at least 150V on the electrolytic, check pin 8 of the
6x5. That is the output of the rectifier circuit. It should be
connected to one of the electrolytic terminals.

Is the sound clear at low volumes? How does it distort as you turn
the volume up, does it just get fuzzy, or does the volume go up and
get fuxzzy at the same time.

The sound becomes also louder.


Bob Hofmann