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 The Mullard and the Kriesler
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 Return to top of page · Post #: 1 · Written at 12:22:04 PM on 13 April 2016.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1098

As promised, here's the story of the resurrection of a Mullard MAS1110, and a Kriesler 11-60.

The Mullard has a brown case, which came up quite nicely once it had been cleaned. The valve line-up was originally 6AN7, 6N8, 6N8, 6M5, EZ82. Upon arrival, the radio had 6AN7, 6V4, 6N8, 6M5, 6V4 respectively. The capacitors were all Philips ones, except the electros. Replaced the errant 6V4 with a 6N8, checked continuity of the speaker transformer, all looked good so applied power. This produced a crackling noise and no reception. The B+ after the choke was only 190 volts DC, and before the choke there was 111 volts AC. Clearly the chassis-mounted 24μF can capacitor needed replacement.

Because this radio uses back-bias, the capacitor case needs to be electrically isolated from earth, and so it is mounted on a small brown standoff, which is screwed down. I removed the capacitor and binned it, and mounted a new one on the standoff, then screwed it back in place. The B+ voltage was now 254 volts, and radio stations could be heard. There was distortion, and this was due to no bias on the 6M5. The 1M ohm and 30K resistors measured 1.5M and 64K, so were replaced. The 2nd 6N8, used as an AF amp, has its screen grid supplied via another 1M resistor, and this had drifted out to 1.7M.

The last problem was that Mr Someone had adjusted everything, so it took a while to get it back in order.

After all that, the sound quality is not very good. I happen to have a white MAS1110, and it sounds a lot better. Back then, I used to draw out the schematics as I worked on a radio. Sure enough, I had one, and I had noted a couple of needed modifications. Next week I will try them out.

The radio originally had a EZ82 rectifier, which are not very common. As it happens, the EZ82 looks exactly like the old, tall version of the 6V4 and has the same pin connections. So I dug out one and put it in, so it looks the part.

The 6N8 also has 2 versions, the old Philips one with the grey solid shield, and the later Miniwatt with the silver mesh shield. I tried swapping some spares around, and all I can say is that the 6N8 is not a very long-lasting valve, with low gain and noisyness being common problems. The Philips version is the more reliable.

One thing to note with the Philips valves, with the silvered pins, the pins get black over time and need to be cleaned with steel wool to restore their appearance. Unlike most valves, the pins are sharp, and the base is flat rather than the rounded one-piece appearance of the usual miniature valve. Valve types that may be encountered are 6AN7, 6AD8, 6N8, 6BH5, 6BD7, 6V4, 6M5, EZ82.

EDIT: I'm informed that these valves are "Innoval" types.

---

Now, on to the Kreisler. This has a black plastic case, and a grey bezel. The dial plate was broken off at some time and been glued back together, however one end had come off again. Valves used: 6AN7, 6AD8, 6M5, 6V4. The 6AD8 had been replaced by a 6N8, which is usually ok, as they are pin-compatible and the 6N8 has more gain.

Again, all capacitors were good quality ones, and in fact no component replacements were needed. Mr Someone had been at work again, and reception was extremely poor, with the low end of the band being completely dead. The was fixed, and with the external antenna it works very well, but with its own 1cm of wire it picks up nothing.

I glued the dial back together, and also the cracked case. This turned out to be a mistake, as I cannot get the chassis fully back in. Something else to look at next week.

Once again, the supplied Miniwatt 6N8 was marginally low gain, a Philips one improved things.


 
 Return to top of page · Post #: 2 · Written at 12:24:06 PM on 20 April 2016.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1098

Finally finished these radios.

The Kriesler's case had minor internal surgery performed, and then the chassis slipped in nicely.

The Mullard MAS1110A had a small mod done: change the feedback cap from the speaker to 1.5pF and it no longer sounds like it's under a pile of clothes.

So I must thank GreatStuff for the donation of these radios, they have turned out fine. Smile


 
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