Leak Stereofetic FM tuner.

[Trevor]

Yes I agree with you have an early A48 in my collection as well as a early Richard Allan class A As to the Armstrong comments I totally agree Ted Rule knew what he was doing
Trev

[PaulR]

I saved for an Armstrong 621 in my teens. Unfortunately when I went to Hardman Radio in Liverpool they had none. The story was that they had so many problems with them that they had sent their remaining stock back to Armstrong for soak testing. I bought a Rotel RX400A instead - I always felt it was a step down from the Armstrong though.

I have since bought a 621 and a 625 and they take a welcome turn in the living room. The 625 has some background noise on one channel which I suspect may be a noisy transistor.

[Jez1234]

There's a soft switch on delay device using bimetallic strip which is their biggest Achilles heal as they were very unreliable but once this is removed and bypassed they can be reliable.

I bought a 625 a year or two back with a view to sorting it out to better than new but the round tuits ran out

[Trevor]

I enjoyed selling the Armstrong 600 series when we could get them ! We had an allocation which was very small I feel this was the reason your sale was diverted to be honest
Trev

[Trevor]

Why they added that thermal switch I will never know it was not on early versions and yes it did give trouble I have shorted lots of them out without any problems ! Loved the modular construction The diode switching was a glance into the future Ok their were problems i did not like the thermal compensation diodes being so remote from the heatsinks but most amps seemed to survive not until the late 70,s early 80,s did the Japs reign supreme re general hifi
Trev

[North hill]

Thanks so much for the tuners information I downloaded the file I will print and put in my radio folder it's always interesting to find out about the design of the leak and Rogers units
Thanks again

[PaulR]

You could well be right, Trevor. They did end up making a sale whereas if they had just said the Armstrongs were is short supply I would probably have waited.

That thermal soft start failed in one of mine but I discovered that it is easily dismantled and works once the points have been cleaned. I did find that the power switch stopped working and could not be dismantled. I got one off a later model and I seem to remember that the earlier one also switched off the DC to make an instant "stop" but the later one only switched the mains thereby fading out as the smoothing cap discharged.

[North hill]

thanks so much for all the information concerning the leak stereofetic and the rogers ravensbourne i will print out the write up i don't know the year about 1970 ?
Here are some pictures, (ROGERS RAVENSBOURNE) the first an inside led filament bulb (2 WATTS) i put in today the power is from the 240ac mains so no power loss from the transformer.
the second picture is an inline mains filter with a 5 watt 30k resister to drop the voltage for the RED LED giving 8mA.
the next picture showing the unit powered up.
The last picture a stereofetic tuning knob i managed to paint with the end of a cable-tie

[North hill]

i have pictures of the LEAK Stereofetic FM tuner with a mains surge Suppressor i used an X rated 275v ac 100nf capacitor in line with a 100.R carbon resister
AND across the mains on the transformer a metal oxide Varistor. with both fitted in the tuner there is less harshness at the top end i did put insulation on the transformer for safety and two mains voltage warning labels.

[Ted Kendall]

I don't think time has been kind to the Armstrong 600 series. When they work, they're fine, but things like the solid core hook-up wire which is now prone to fractures and dry joints and the way the meters get cooked by their bulbs can make them infuriating to fix. Of course,, they aren't the only classic hi fi to be ever so slightly in advance of the available technology.

[North hill]

Having troubles with the right hand output now and then I get pos hissing like a faulty electrolytic capacitor or a faulty transistor I did change the output to NPN BD139 for left and right into new 10uf non-pola capacitor.has one of the cd blocking caps gone down ? It's a fault that is not all the time it comes and goes


Any suggestions

[North hill]

I did change the new caps after the stereo multiplex filter the right channel is still popping and hissing now and then i will change two transistors BC185L TO THE SAME TYPE i did make an order online for 10. i dont think the ceramic caps are a problem but you never know as it is the right channel i know it is after the multiplex filter.

[North hill]

I made new fills for the front of the stereofetic FM tuner I used Corel draw 11 the texture fill looks like water waves or radio waves. I did measure the thin metal plate for the correct dimensions

[North hill]

Eventually I have solved the popping and hissing on the left channel I replaced the BC184L transistors driving the 38khz trap filter and the 1.9nf caps to polyester across the inductor with all the component changes the tuner is a lot smoothe lower distortion especially in the high frequency.. the tuning scale print is a test to check the correct placement and size through the hole in the original metal sheet

[Jez1234]

Ideally you should now readjust the inductor cores to give best suppression of pilot tone etc combined with best frequency response.

[North hill]

Thanks for the advice.

[North hill]

The new stereofetic plate arrived this week The finish is very clear. One end has come away I used Double sided tape.