KB KP043 record player

[kirstyd]

I recently saved this from certain destruction .The amplifier is fine but its 8 by 5 inch 15 ohms [i think] speakers are missing .they have been replaced with smaller ones which are totally unsuitable [i have already posted in the parts section for those] The original cartridge has also been removed and one of those Chinese thing glued in place .It wont play a record because the arm is too light and the cart is at the wrong angle .I can easily fit a new BSR cart but i would like to know what would have been fitted originally.Anyone know?.Thanks guys K

[Restoration73]

BSR C109 fitted with Acos GP93/1 cart.

[Techman]

I think they used a Sonotone in that player too.

If you're not going to play 78s, then just re-set the position of the existing cartridge and adjust the tracking weight of the arm to match it.

[Edward Huggins]

A good idea to re-set the tone arm for the cartridge to weigh at c.4/5 grams.
Finding 8" x 5" 15 ohm speakers might be a challenge.
Scrap ellipticals from a car breaker are liable to be only 4 ohms.
A good source for the correct speakers will be in the many 1970s Thorn built Stereograms. They nearly all seemed to use this size - 8 to 15 ohms.

[Nickthedentist]

I was thinking the same. There are sometimes speakers pulled from scrapped radiograms offered on eBay for sensible sums.

Also, the horrid plastic speakers supplied with some 1970s UA-series Fidelity stereos have drivers that would do.

Well done for saving this, it looks like quite an unusual and rare machine and should sound good.

Nick.

[crackle]

This would be an ITT-KB KP043 as its production date c.1969, falls just after the introduction of the ITT brand to the KB brand name, but before the KB part was dropped altogether which was around c. 1972.
If you require a bit more detail on the circuit layout, the manufacturers service manual is available on my KB Museum website.
There is a manufacturers recommendation to change the routing of the mains cable which is included in the service data.
Good luck with finding a couple of suitable speakers.
Mike

[kirstyd]

i have just found a couple of [right size] speakers but they only measure 12 ohms [original speakers were 15 ohms] when i put a meter on them .Would they do the job or would they damage the amp ?

[Edward Huggins]

If I were you I would use these. They are unlikely to damage the amp at all and the impedance mismatch can be tolerated. You have been lucky to find these. Hoping they have a good cone excursion.

[ms660]

Originally Posted by kirstyd

i have just found a couple of [right size] speakers but they only measure 12 ohms [original speakers were 15 ohms] when i put a meter on them .Would they do the job or would they damage the amp ?

The original 15 ohms is 15 ohms impedance, if you measure the resistance with a meter the resistance should be lower than the impedance. As a rough guide for an unknown loudspeaker impedance add 1/5th to its measured DC resistance....14.4 ohms....near enough.

Lawrence.

[kirstyd]

OK guys thanks for that I will try them and see what they sound like.

[Sideband]

Chances are you have nominal 15 ohm speakers there. As has been said, the DC resistance as measured on a testmeter will be lower than the AC impedance.

[kirstyd]

Hi al.

Well I managed to get two speakers from a scrap HMV stereogram. They are fitted into the cabinet. On connecting the amplifier everything works well with good sound [CD player connected to the DIN socket] but the bass control makes absolutely no difference to the sound. On closer inspection I found the two pick up leads [red and black third photo] from the DIN socket were touching causing the sound to be mono. Once separated we have stereo back but still no difference in sound when adjusting the bass. At first I thought maybe a rectifier problem but I am getting a good 22/23 volts DC from it. Any ideas guys?

No you're not seeing things the cabinet is now covered in red rexine. The teak veneer cabinet was past repair.

[crackle]

I dont think the bass control will work with a low impedance source like a CD player. It is designed to work with a high impedance ceramic or crystal pickup. I believe, by altering the load on the pickup it effects the tonal characteristics of the pickup elements.

Mike

[kirstyd]

Yes I see what you mean. The leads from the five pin DIN are connected to one set of connections whilst the leads from the cart pick up are connected to another that do respond to the bass control. While the unit works OK with a good output from both channels there is a constant rustling sound on one channel. Also when I turned the amplifier over can you believe the transistor I am pointing just fell out. I have since soldered it back in. Any ideas on the rustling sound guys?

[crackle]

It sounds like one of the output transistors has gone noisy. This is where a signal tracer comes in handy.
Does it still sound noisy if you remove the BC187 driver transistor?

Mike

[kirstyd]

will have another look at it at the weekend and let you know

[kirstyd]

there isnt a BC 187 .

[crackle]

My reason behind suggesting remove the driver transistor, (BC187 on the service document) was to see if the noise is generated in the germanium output pair.
With the driver removed there should be no noise from the output, if there is then one or both of the output transistors is faulty.
OK, so it looks like either someone has changed the BC187 to a BC261, or KB decided to use a different transistor, no matter the same idea should work to remove the pre-amplifier stages, (with their potentially noisy resistors and breaking down capacitors) and just test the output pair of transistors.

Mike

[kirstyd]

Well you were right .I replaced both of those transistors with new ones and bingo the rustling has gone just a good healthy buzz when touching the pickup leads.All i need to do now is find a suitable cart.I have three Acos GP93[i think]carts all with the same fault [they sound terrible until you put some weight on them then they give good sound .I have dismantled a BSR cart and cleaned its internal contacts with good results so i am going to attempt the same with one of the Acos carts will let you all know how i get on [my eyes are not what they were].Thanks everyone for the usual expert advice

[crackle]

I dont know the ideal tracking weight of the GP93, but some of the older cartridges did need to track at 4 or 5 grams, which is quite a lot compared to modern magnetic ones.
I am glad you have got the amp working. Did you do the test I suggested and did it show the noise was coming from the OP transistors.

Mike