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Forum 141

Circuit mistakes.

General Technical Discussion

Last Post by Terrykc 5 years ago

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Nuvistor

(@nuvistor)

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I came across these anomalies while looking at some circuits, the circuit is for a Melodyn VTR4900, R4901 range of radio grams.

The first problem although not really a problem is showing the EAF801 as a double diode triode, with pin 7 shown as a diode anode not an internal screen, it’s connected to chassis.

Another potentially more serious error is the ECC84 in the VHF tuner, the valve connection match the more likely ECC85.

It does appear to be a nice radio/gram with the common valve line up, ECC85, ECH81, EAF801, ECL86, EM87, 2x OA1172 ratio detector, selenium full wave bridge, standard speaker and tweeter and tape skt.

Mistakes in circuits are common, I am sure they have caught many of us out.

Frank

Posted : 07/07/2019 7:33 pm

sideband

(@sideband)

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Posted by: Nuvistor

It does appear to be a nice radio/gram with the common valve line up, ECC85, ECH81, EAF801, ECL86, EM87, 2x OA1172 ratio detector, selenium full wave bridge, standard speaker and tweeter and tape skt.

I wouldn't say EAF801 was that common?

Posted : 08/07/2019 10:57 am

Nuvistor

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Perhaps not but it’s a basic diode triode and that type was a standard valve type.

But yes perhaps I should have pointed that out.

Frank

Posted : 08/07/2019 11:01 am

Terrykc

(@terrykc)

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Posted by: sideband

I wouldn't say EAF801 was that common?

Perhaps not in the UK but could have been popular on the continent. Take the EL95, for example. Used for years in everything that Grundig produced but never by a UK manufacturer. In fact, it was classified as an industrial type here which made it the only valve fitted in a domestic product which didn't attract Purchase Tax!

My guess is that this set was first produced using the ECC84, EAF801 line-up but when the ECC85 and EBF80 came along, they started being used in production and the schematic was modified accordingly - but someone forgot to alter the annotations!

When all else fails, read the instructions

Posted : 09/07/2019 1:01 pm