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Old 16th Aug 2019, 9:58 pm   #41
ms660
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Default Re: Shaftesbury 519 amplifier

Did you measure it out of circuit?

Lawrence.
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Old 16th Aug 2019, 10:09 pm   #42
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Default Re: Shaftesbury 519 amplifier

In this instance no. I have to say it a component I’ve not seen before in any vintage instrument.
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Old 16th Aug 2019, 11:33 pm   #43
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Default Re: Shaftesbury 519 amplifier

It's the colour coding that might be new to you, it can be read in the same way as the body, tip, dot code that's used on the old dog bone resistors, eg: body>>tip>>dot except in this case it's body>>end ring (tip)>>middle ring (dot) which represent in that order....the 1st number>>the 2nd number>>the multiplier.

The colours represent the same numbers found in the usual resistor colour code that you will have come across eg: Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4 etc etc.

In your example:

Body = Orange = 3

End ring = Orange = 3 (same colour as the body therefore no ring is visible)

Middle ring = Red = 2

So, 1st number = 3, 2nd number = 3, multiplier = 2, therefore the value represented is 3300 Ohms (3.3k)

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Old 17th Aug 2019, 8:53 am   #44
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Default Re: Shaftesbury 519 amplifier

And the silver end is the tolerance identifier. Looks like it's in parallel with an electrolytic capacitor, hence the confusing reading. It'll read as a resistor if you use an analogue multimeter using dc for its resistance measurements.
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Old 17th Aug 2019, 5:30 pm   #45
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Default Re: Shaftesbury 519 amplifier

Correct...it’s one of the very few resistors anywhere being near or in tolerance. It feels like a complete component rebuild as they are so far out. I’m not overly bothered now as I do intend to use it at home.
The 16uF UCC electrolytics appear to have perished rubber(?) body seals so I’m in two minds whether to replace or not?
There is a very small brown Hunts cap that is connected on the underside of the chassis that is connected between the base of the ECC83 and EL84 marked at 500 600v. Any idea what the value is ? I’ve not tested it as I’m not convinced it will give a true reading.

Best regards

Rob
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Old 17th Aug 2019, 6:21 pm   #46
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Default Re: Shaftesbury 519 amplifier

Quote:
There is a very small brown Hunts cap that is connected on the underside of the chassis that is connected between the base of the ECC83 and EL84 marked at 500 600v. Any idea what the value is ?
From the layout drawing you posted and your photo it looks to be the coupling capacitor between the 1st anode (a1) of the ECC83 and the control grid (g1) of the EL84, the value given in the layout drawing appears to state 360pF so far as I can make out, as a first guess I would say the one in yours is 500pF.

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Old 17th Aug 2019, 6:42 pm   #47
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Default Re: Shaftesbury 519 amplifier

Many thanks Lawrence
I will test anyway to check

Best regards

Rob
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Old 17th Aug 2019, 7:27 pm   #48
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Default Re: Shaftesbury 519 amplifier

Tested out of circuit....800+ pF??
I’ve got nothing that small in value at 600v as polyester or similar..any suggestions?
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Old 17th Aug 2019, 7:30 pm   #49
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Default Re: Shaftesbury 519 amplifier

Can you post a photo of the said capacitor showing all the markings?

Lawrence.
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Old 17th Aug 2019, 7:49 pm   #50
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Default Re: Shaftesbury 519 amplifier

Pics of small brown hunts cap
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Old 17th Aug 2019, 7:58 pm   #51
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Default Re: Shaftesbury 519 amplifier

does it matter what the cap composition is for use as a coupling cap? I probably can find some mica caps that Im sure that I have (old RS ones)?
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Old 17th Aug 2019, 8:06 pm   #52
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Default Re: Shaftesbury 519 amplifier

470 pF would be the nearest modern value, lots on the web, eg:

https://www.cricklewoodelectronics.com/C2K470P.html

Other suppliers are available.

EDIT: Post crossed.....If you have a mica type it will be ok if it's in good condition, as in not leaking....remember that a leaking capacitor in that circuit position is bad news.

Lawrence.

Last edited by ms660; 17th Aug 2019 at 8:14 pm.
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Old 17th Aug 2019, 9:10 pm   #53
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Default Re: Shaftesbury 519 amplifier

I’ve order one to be the safe side. If found some old 25uF 25v electrolytics which have a value of 28uF....replacement for the Plessey one?
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Old 18th Aug 2019, 8:04 am   #54
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Default Re: Shaftesbury 519 amplifier

500p as a coupling cap! It's going to sound pretty shrill, I'd be tempted to put in a 10n or similar at least to get it running.

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Old 18th Aug 2019, 5:53 pm   #55
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Default Re: Shaftesbury 519 amplifier

Ok, I’ve replaced all of the Hunts on the bottom chassis section and put a 1000pF polyester as the coupling cap to start with (630v). The resistor tolerances are much better so I’ve not replaced any. The red and black Plessey electrolytic has been replaced with a .47uF 50v cap. Would you leave the 3 remaining metal electrolytics in place if they work? I’ve also yet to try the UCC smoothing cap but do have a JJ Tesla replacement if needed.
I’m also not sure about the old red 200R power resistor....I’m sure I’ve read somewhere to replace these with a 5 watt power resistor or similar but I could be mistakenly?
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Old 18th Aug 2019, 6:30 pm   #56
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Default Re: Shaftesbury 519 amplifier

Quote:
Originally Posted by Guitarist28 View Post
The red and black Plessey electrolytic has been replaced with a .47uF 50v cap.
Which red and black Plessey electrolytic...there's two of them?

What are their values?

.47uF 50v cap....0.47uF? or 47uF?

Lawrence.
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Old 18th Aug 2019, 6:33 pm   #57
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Default Re: Shaftesbury 519 amplifier

Yes replaced both - 50uF 12v, with 47uF 50v (smallest I had).
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Old 19th Aug 2019, 4:41 pm   #58
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Default Re: Shaftesbury 519 amplifier

Quote:
Originally Posted by Diabolical Artificer View Post
500p as a coupling cap! It's going to sound pretty shrill, I'd be tempted to put in a 10n or similar at least to get it running.
Ah, but remember the output of a guitar is much greater on the bass strings that move much more in the pick-up field than the treble strings, some form of EQ is needed to even get a flat response, easily (cheaply) done with quite small coupling caps.

Indeed, look at some of the classic Fender circuits and the pre-amp/phase splitter coupling is indeed 500pF; some fairly small values in the pre-amp tone circuits too.

Fender used to use a "Bright" switch too, nothing more than 120pF switched between the high end of the vol pot and the slider and my word, does that give the top 3 strings some bite, and a fair amount of hiss too!

Similarly if you try an electric guitar through a conventional Hi-Fi amp it will sound very muddy, dull and inarticulate, bass pot to zero and treble to max helps a bit.

R.
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Old 19th Aug 2019, 4:44 pm   #59
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Default Re: Shaftesbury 519 amplifier

Thanks Richard,
As you can see, I've started with a 1000pF but have a 500pF on order (I have nothing that small a value at 600+volts)
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Old 19th Aug 2019, 5:04 pm   #60
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Default Re: Shaftesbury 519 amplifier

The Pye P45RG radiogram had a 500pF coupling capacitor in circuit when the tone selector was set to "bright"

Lawrence.
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