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Old 28th Jul 2019, 9:23 pm   #1
HedleyH
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Default Bush SRP31C restoration

I am a recent proud owner of a Bush SRP31C.
The usual common issues exist with this model. I have ordered 2 x 47uf 63v capacitors to replace the original Plessey components. 1 of these read at 55, the other was way out so I'm replacing both.
I have tested the rectifier which is outputting 78vdc, a little low according to other posts I have read on here. To replace this I have ordered a IN4007 diode but am unsure which resistor to choose to accompany it. Looking at other threads, values varying between 100 ohms to 330 ohms have been used. Which would be most suitable? Any advice would be greatly appreciated.
The unit actually sounds rather good (especially compared to my fathers old Regentone player). The tweeter is certainly dead and I have stripped the Garrard and cleaned, lubricated all cams bearings etc. The idler could do with renewing as it continues to slip when the tone arm returns. Very happy so far and I hope to repair as necessary and enjoy it for years to come.
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Old 28th Jul 2019, 10:04 pm   #2
Edward Huggins
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Default Re: Bush SRP31C restoration

You do not need to "renew" the idler, just skim/sand the edge so that it provides more grip. Use a lathe or a drill with a sander.

The player will still sound quite good, even if the old electrostatic tweeter has failed - as they do. The rather small 6" x 4" Celestion will actually give a smoother treble resonse just on its own.

As regards the series resistor with the new rectifier, 330 ohms will be fine.
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Old 29th Jul 2019, 8:58 am   #3
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Default Re: Bush SRP31C restoration

Hello and welcome the SRP 31c is a great machine and we'll worth the effort to get it back to good working condition.
The resistor I normally use with the in4007 is 275 ohms I think you'll find a 100 ohm will run a little hot.
The tweeter can be repaired there are a few videos on YouTube on how to fix these but to be honest I have fixed a few and it doesn't make a lot of difference to the sound.
With the idler have you tried redressing it, the idler on the Garrard decks can be very troublesome I usually end up remanufacturing them or you could have it re rubbered if you can't find a decent one out there.
Good luck Les.
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Old 29th Jul 2019, 9:57 am   #4
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Default Re: Bush SRP31C restoration

Surely 275R will run hotter (or at least dissipate more) than 100R? The current won't vary by much and the power dissipated will be proportional to the resistance- Isquared*R.
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Old 29th Jul 2019, 10:09 am   #5
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Default Re: Bush SRP31C restoration

By my calculations if, e.g., 200mA is drawn via 100 ohms, the dissipation will be 4 watts, but 200mAx2 divided by 275 = 1.45 watts approx. I've always used P=IV to find wattage, but the results end up the same by this method
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Old 29th Jul 2019, 12:32 pm   #6
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Default Re: Bush SRP31C restoration

Quote:
Originally Posted by 'LIVEWIRE?' View Post
By my calculations if, e.g., 200mA is drawn via 100 ohms, the dissipation will be 4 watts, but 200mAx2 divided by 275 = 1.45 watts approx. I've always used P=IV to find wattage, but the results end up the same by this method
?

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Old 29th Jul 2019, 12:39 pm   #7
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Default Re: Bush SRP31C restoration

I think what Les meant was that the record player would run too hot with 100 ohms, which is far too low a value!

A 4 watt resistor is really too low a power rating, regardless of its 'ohms' value, as although it will work, it will run very hot and may scorch nearby components and wiring, so throw the calculations out of the window on this one and go for at least 7 watts.

It's been several years since I last worked on one of these, so I've forgotten the exact value of resistor required and it's a bit variable anyway set to set, depending on emission of the valves etc. You'll soon know if you've got the wrong value as when you measure the HT voltage as described in the service information, you'll find it to be incorrect, so you'll have to buy another resistor of the appropriate value to correct it - I always keep a stock so that I can try several different values until the voltage is 'approximately' correct.
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Old 30th Jul 2019, 11:32 am   #8
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Default Re: Bush SRP31C restoration

Yes Techman that is what I meant but forgot to mention the wattage, silly me.
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Old 30th Jul 2019, 12:56 pm   #9
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Default Re: Bush SRP31C restoration

Quote:
Originally Posted by 'LIVEWIRE?' View Post
By my calculations if, e.g., 200mA is drawn via 100 ohms, the dissipation will be 4 watts, but 200mAx2 divided by 275 = 1.45 watts approx. I've always used P=IV to find wattage, but the results end up the same by this method

Yes 200mA through 100R is 4W (0.2x0.2x100) but 200mA (same current) through 275R will be 0.2x0.2x275 which is 11W


The calculation is IxIxR (IsquaredR) not Ix2xR (2IR) nor 2I/R nor (IxI)/R .


Back to P=IV and V=IR (R=V/I) then if you sub IR for V in P=IV you get P=IIR and also subbing V/R for I you get P=VV/R


Lots of fun with a bit of algebra!
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Old 30th Jul 2019, 7:54 pm   #10
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Default Re: Bush SRP31C restoration

Thanks for all the advice and comments so far. Just waiting on the postman to deliver the bits then I'll begin replacing them. I ended up ordering 270 ohm, 5 watt resistors and will see how they perform.
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Old 13th Aug 2019, 10:05 pm   #11
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Default Re: Bush SRP31C restoration

Quick update so far. I ended up using a 330ohm 10 watt resistor. This is giving 212VDC so looking good. Have also replaced the two Plessey capacitors. The result is more bass, better volume control and also possibly less distortion at higher volume.

The cartridge may not be the best, Acos GP91 3SC. I'm waiting on delivery of a BSR SC11M . Any advice on the best way to wire up the 4 pins would be appreciated.
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Old 14th Aug 2019, 11:32 am   #12
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Default Re: Bush SRP31C restoration

The Acos GP93-1SC was not the originally fitted cartridge and this will overload the amp - and possibly cause distortion.
The LH and RH channels must be bridged on the BSR cartridge to provide a mono signal. Even so, that Acos cartidge is a rare, high-output, stereo-compatible type and is worth quite a lot in its own right.
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Old 14th Aug 2019, 12:12 pm   #13
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Default Re: Bush SRP31C restoration

Quote:
Originally Posted by HedleyH View Post
I'm waiting on delivery of a BSR SC11M. Any advice on the best way to wire up the 4 pins would be appreciated.
you can do this at either end of the tone arm wires by merging the wires of both channels together
but never solder direct on to the cartridge pins
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Old 14th Aug 2019, 1:04 pm   #14
Edward Huggins
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Default Re: Bush SRP31C restoration

Sorry, in my Post #12 I meant to write Acos GP91-3SC.
You should bridge/sum LH+ and RH+, and then, LH- to RH-.
It might be easier to do this on the pick up wiring tag card underneath the Garrard autochanger.
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Old 14th Aug 2019, 1:05 pm   #15
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Default Re: Bush SRP31C restoration

It's a long time since I worked on one these - 50 years, in fact! - but, unless my memory is deceiving me, there is a coax socket at the rear of the motor board with a short link lead and plug. This was provided for the connection of an optional external amplifier for stereo.

In mono mode, the plug stays in the socket, thus connecting the two channels together.

So, one channel should be wired directly to the amplifier and the other to the socket arrangement at the back but, even if a mono cartridge has been retrofitted, there would be no reason to modify the wiring beneath the deck.

Details of the cartridge connections to the head shell plug can be found in the manual on the Radio Workshop site but I can't get the link to work.

There is no need to modify the wiring in the arm.

You may also find the information in this thread of use: https://www.vintage-radio.net/forum/...3&postcount=16
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Old 14th Aug 2019, 1:21 pm   #16
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Default Re: Bush SRP31C restoration

Quote:
Originally Posted by terrykc View Post
It's a long time since I worked on one these - 50 years, in fact! - but, unless my memory is deceiving me, there is a coax socket at the rear of the motor board with a short link lead and plug. This was provided for the connection of an optional external amplifier for stereo.

In mono mode, the plug stays in the socket, thus connecting the two channels together.

So, one channel should be wired directly to the amplifier and the other to the socket arrangement at the back but, even if a mono cartridge has been retrofitted, there would be no reason to modify the wiring beneath the deck.

Details of the cartridge connections to the head shell plug can be found in the manual on the Radio Workshop site but I can't get the link to work.

There is no need to modify the wiring in the arm.

You may also find the information in this thread of use: https://www.vintage-radio.net/forum/...3&postcount=16
as above then
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Old 14th Aug 2019, 2:48 pm   #17
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Default Re: Bush SRP31C restoration

That's good information, but in this case the OP has been using it with just a 2 wire connection to the Acos GP91-3SC cartridge and henwill need the full 4 wire connection to the replacement incoming BSR SC11M.
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Old 14th Aug 2019, 5:18 pm   #18
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Default Re: Bush SRP31C restoration

Quote:
Originally Posted by Edward Huggins View Post
The Acos GP93-1SC was not the originally fitted cartridge and this will overload the amp - and possibly cause distortion.
The LH and RH channels must be bridged on the BSR cartridge to provide a mono signal.
The cartridge feeds into the amplifier via the volume control so cannot overload the amp (unless the control is advanced too far!)

Bush built the Mono/Stereo bridging into the design so no bridging is needed elsewhere.
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Old 16th Aug 2019, 6:13 pm   #19
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Default Re: Bush SRP31C restoration

Have fitted the new BSR SC11M cartridge and although the sound is nice and crisp along with good bass, it's rather quiet. Looking at the output specs for the original GC8 cartridge fitted to these, I maybe should have stumped for a BSR SX6M or similar. These appear to have similar output.
I was unsure the tweeter was functioning but there is noticeable sound coming from this(albeit very quiet) since removing the old Acos and fitting the BSR.
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Old 16th Aug 2019, 10:30 pm   #20
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Default Re: Bush SRP31C restoration

It will be a bit quieter because a medium output ceramic cartridge has less output than the equivalent crystal cartridge which would have originally been fitted, such as the GC8. To get the same output you'd have needed the BSR SC11H version, but these are no longer available. As I type this, I've actually got a Bush SRP31C record player fitted with a BSR SC12M on the table in front of me and I've just been playing an LP on it and I would say that the volume is 'adequate'. However, I've just tried the same record on a PYE Black Box fitted with a BSR X5M medium output crystal cartridge and there's absolutely bags of gain on this combination. So the advice would be to get one of these cartridges, but keeping in mind that although they're stereo compatible and therefore safe to play stereo records, the output from them is 'mono', so you wouldn't be able to get stereo reproduction from the 'add-on' additional amplifier, if you happened to have one.
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