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Dynatron 1275A series - schematic or help!

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Doz
 Doz
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Hi All,

I've got a Dynatron 1275A on the bench, with an amplifier module blowing fuses. It's a simple amp with a pair of BD103's as output.

There's a driver transistor, Q207 which is dead short. What is it (was it)? It's only markings are 1113 and a date code 7503

Any info greatly received... 

 
Posted : 30/06/2018 4:36 pm
crustytv
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Hi Andy,

I've got the data, I'll get scanned for you  ? 

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Posted : 30/06/2018 4:49 pm
Nuvistor
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This web page claims to have a circuit but you need to join, I am not a member so cannot confirm if it’s correct.

http://www.diyaudio.com/forums/parts/218868-amps-1975-dynatron-1275a-quad-405s.html

The other thought is it a 2SC1113

https://www.el-component.com/bipolar-transistors/2sc1113

 

Frank

 
Posted : 30/06/2018 4:53 pm
Nuvistor
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There you are a Chris to the rescue  ? .

 

Frank

 
Posted : 30/06/2018 4:54 pm
crustytv
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Data is now in the library

CrustyTV Television Shop: Take a virtual tour
Crusty's TV/VCR Collection: View my collection
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Crusty's 70s Lounge: Take a peek

 
Posted : 30/06/2018 5:03 pm
crustytv
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According to my data the driver is a 2sc1115 140/80V, 10A, 100W, 10MHz

eqiuvs are BD245D, 2N3442, 2SD551, 2SD1047, KT864A

Note: your fitted 2sc1113 120/100V, 6A, 40W, 10MHz

equivs BD243C, BD543D, MJE 15028, 2SD866, 2N6372, KT808A

CrustyTV Television Shop: Take a virtual tour
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Posted : 30/06/2018 5:20 pm
Nuvistor
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Dynatron started to use a peculiar mix of transistors in the 1970’s, being a Dynatron dealer we used to get exact replacements from them. I would have thought they would have stayed with Mullard seeing that they were all under the same umbrella company.

Frank

 
Posted : 30/06/2018 5:45 pm
Doz
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It certainly isn't a 2SC1113, as it's a TO-5 can (I should have mentioned that earlier!) The circuit diagram (thanks Chris and Frank!) shows a C1131 , which isn't a 2SC1131 either, as that's also a TO-66

 

 

 
Posted : 30/06/2018 5:54 pm
Doz
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So, the diagram show as an MA8003 as the complimentary TR206, which is :

Type Designator: MA8003

Material of Transistor: Si

Polarity: NPN

Maximum Collector Power Dissipation (Pc): 0.8 W

Maximum Collector-Base Voltage |Vcb|: 80 V

Maximum Collector-Emitter Voltage |Vce|: 60 V

Maximum Emitter-Base Voltage |Veb|: 7 V

Maximum Collector Current |Ic max|: 0.8 A

Transition Frequency (ft): 50 MHz

Forward Current Transfer Ratio (hFE), MIN: 100

Package: TO5

So all I need to find is the PNP equivalent 🙂 BC557 or similar...

 

 

 
Posted : 30/06/2018 6:02 pm
Nuvistor
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Do the other transistor types in the circuit match the ones in the amp?

Edit, what transistors are in the other amplifier?

Frank

 
Posted : 30/06/2018 6:18 pm
PYE625
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Like a dumbo, for years I used to wonder what "Ether Stereo" was on some Dynatron radiograms ....I used to think it meant "either" stereo or mono !!

Now the penny finally has dropped,  it is of course stereo FM radio.....unless I'm mistaken.  ? 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 30/06/2018 6:46 pm
Nuvistor
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I don’t remember seeing that label, still I was fixing the things. The more expensive amplifiers were decent but the less expensive ones ( notice I didn’t say cheap) were not that great in build quality but they sounded good.

Dynatrons in the 1970’s were sold for their cabinet, Queen Anne style etc. If one half the partnership wanted a Hi-Fi in the house, the cabinet had to suite the other partner.

I will leave it as which half was which.

Frank

 
Posted : 30/06/2018 6:57 pm
Cathovisor
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Posted by: PYE625

Like a dumbo, for years I used to wonder what "Ether Stereo" was on some Dynatron radiograms ....I used to think it meant "either" stereo or mono !!

Now the penny finally has dropped,  it is of course stereo FM radio.....unless I'm mistaken.  ? 

Dynatron were very fond of the "Ether" prefix - it goes right back to the early 30s. Pity they became little more than Ekco/Pye/Philips in a posh frock in the end - enough to make the Hacker brothers start production under their own name shortly afterwards!

 
Posted : 30/06/2018 7:51 pm
Doz
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Posted by: Nuvistor

Do the other transistor types in the circuit match the ones in the amp?

Edit, what transistors are in the other amplifier?

Both amps are identical. It matches the circuit, except for that one number.

 

 
Posted : 01/07/2018 11:12 am
Nuvistor
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Any resistor burn up? 

I am using my phone so not really able to look at the circuit. My  iPad has been commandeered by the granddaughters and all have gone to birthday party.

If I get it back today I will check the circuit again. 

Frank

 
Posted : 01/07/2018 2:24 pm
Doz
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Posted by: Nuvistor

Any resistor burn up? 

I am using my phone so not really able to look at the circuit. My  iPad has been commandeered by the granddaughters and all have gone to birthday party.

If I get it back today I will check the circuit again. 

Nope. I'll dig out sensible PNP later if the workshop cools down and see what happens.

 
Posted : 03/07/2018 11:33 am
Doz
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Well, In went a BC559 ... set up the bias, and it's been running happily at about 10 watts into a load for hours 🙂

 
Posted : 03/07/2018 8:07 pm
PYE625, PYE625 and PYE625 reacted
Nuvistor
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Excellent, presume just old age with the transistor going short then. Luckily nothing else got damaged, get one go and it’s very often a chain reaction.

They sounded very good, not classed as true HiFi but certainly a nice sound.

Frank

 
Posted : 03/07/2018 9:18 pm
Doz
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Turned out nice again 

 

http://andydoz.blogspot.com/2018/07/sam-and-queen-anne-dynatron-1275a-series.html

 
Posted : 08/07/2018 6:03 pm
Nuvistor
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I don’t remember there being a general problem with hum with these sets, not enough for customers to complain about,  I do remember the slider controls gave problems though. 

They were sold on cabinet design we had just as good or better products for less money but not with the same styling. Customers came into the shop specifically for the cabinets.

So has it pride of place in the house?

 

Frank

 
Posted : 08/07/2018 6:37 pm
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