Replacement for BEL PT4 & PT6 Needed

[anirban420]

Hi folks,

I have a HMV STEREO 666 Record player. It is a 1976 model. It has a Push-Pull Class AB amplifier. Its two main amplifying transistors are...

BEL
PT4
AX6

and.....

BEL
PT6
SX5

I need to replace those transistors because they are gone. I have searched many places and they are not available locally. Can it be found anywhere or do these have any replacements? Thumbnails of these transistors are attached herewith....

 

[JonSnell Electronic]

What is it out of and can you measure a good one to see if Si or Ge type?

 

[anirban420]

Thanks for the reply Jonsnell 🙂. I have found no details of these transistors over the internet or anywhere. Since other transistors found in these system are of Ge type (eg. AD148) there is a possibility of these pair might be a Ge type, but not sure.

 

[anirban420]

What is it out of and can you measure a good one to see if Si or Ge type?

I have just checked the other transistors in the record player. There are BC148B and BC187. They are all Si type general purpose transistors. But what about my transistors of concern??????

BC148B Datasheet....

bc107_bc108_bc109_bc147_bc148_bc149.pdf PDF datasheet

BC187 Datasheet

http://www.sonlineshop.com/datasheet/Transistors/bc 187,188.pdf

 

[Dissi]

They seem to be germanium power transistors, replacements are NTE155 and NTE121:

PT4 NTE Equivalent NTE155 TRANSISTOR NPN GERMAN... - Wholesale Electronics
PT6 NTE Equivalent NTE121 TRANSISTOR PNP GERMAN... - Wholesale Electronics

Edit:
Here they say the NTE131 is complementary to the NTE155:
http://www.nteinc.com/specs/100to199/pdf/nte131.pdf 😕

 

[Dissi]

The original specifications:

PT4 Spec Sheets Details Diodes, Transistors, Thyristors, Triacs, Diode Array, Integrated Circuits and Semiconductors — Product Line
PT6 Spec Sheets Details Diodes, Transistors, Thyristors, Triacs, Diode Array, Integrated Circuits and Semiconductors — Product Line

 

[anirban420]

Thanks Dissi for your replay. At last you have given me a insight about the transistor. Thanks a lot. So, what should be the replacement for the PNP one, NTE121 or NTE131? Is it somehow available in India?

 

[khalsa]

use 2n3055,2n2955

 

[anirban420]

use 2n3055,2n2955

Actually I want to hear the ORIGINAL SOUND QUALITY of the player. I never heard the player at its optimum quality. The set is presently dead. When it was alive it gave a very high pitched, noisy high frequency output that had no detail, and it had a serious lack of bass. I am not expecting some Boomy Bass and crisp high frequency detail. The sound of the player was audible, but lacks a lot of thing that cannot be explained by writing here......

I doubt 2N3055/2955 can power up the system or not. If they can do, the sound quality will not be changed?

I am attaching the schematic of the main board of the player. Any suggestions are heartily welcome. Sorry for the hand drawn schematic. I made this when I was 14 😀 and no computers were there. Some capacitor lacks value. Those are in the audio signal line. I have doubt about the values of those caps because the original caps were always missing. Using 0.1MFD gives a creepy sound. The pre-amp part is OK, I have checked it with different amplifier. It may be for some component fault in amp section, but not sure. Presently I am using 0.047MFD for all caps. Any suggestion about the value of those cap? A serious inspection is needed for finding the fault.......

 

[Madaudio]

3055/2955 cnnot be used. this amp is not of much sound quality. best option is to use a new dc coupled amp.

 

[reubensm]

This is an old thread but posting for the benefit of those who find this later, while searching for PT4/PT6 info on the internet (specifically for repairing Philips and HMV low power amplifiers in record players, sold in India in the 1970s)

PT4 and PT6 were manufactured in India by Philips (now NXP) and BEL (Bharat Electronics limited) for use as power transistors in small 5-7 watt amplifiers. Obviously you will not be able to find replacements for these. These are actually Indian versions of the European germanium pair, AD161/AD162. Philips commonly used the AD161/AD162 pair in many of the smaller powered amplifiers and record players in the 1960s and 1970s. Perhaps the most famous example of a small amplifier from Philips using this pair is the 22RH580 from 1968. One of the highest quality amplifiers in this low power range. The AD161/162 pair is still available, particularly on ebay.de
Regards