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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 11th Aug 2019, 7:36 pm   #21
Guitarist28
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Default Re: Shaftesbury 519 amplifier

Wow... Truly stuck now. I've 2 x 1/4į chassis nuts that in such an awkward place at the rear of the chassis. I was hoping to remove the speaker but the power transformer is the way in order ro get to the nuts. It certainly wasn't built with repairs in mind.
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Old 12th Aug 2019, 6:23 pm   #22
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Default Removal of awkwardly placed nuts

Iím really open to some suggestions. There are 2 1/4 chassis nuts on an amp I am trying to restore. They are close to the front speaker baffle but the power transformer on the chassis is blocking the removal of the speaker. This would really help to get to one of the nuts.
The amp is a Shaftesbury 519, there is a thread with pics on the forum already.
I donít want to break anything before Iíve even started to replace anything.

Any help will most appreciated

Best regards

Rob
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Old 12th Aug 2019, 6:53 pm   #23
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Default Re: Shaftesbury 519 amplifier

You may find that if you unbolt the mains transformer from the chassis, this will give sufficient "wriggle room" to enable you to access the nuts.

Alternatively you may be able to use a custom spanner made by filing a slot in a piece of thin mild steel.
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Old 12th Aug 2019, 7:11 pm   #24
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Default Re: Shaftesbury 519 amplifier

You shouldn't have to unbolt the mains transformer to remove the chassis, look at the chassis's front lip on here, is yours the same ?:

http://www.vintagehofner.co.uk/amps/shaft1.html

Lawrence.
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Old 12th Aug 2019, 7:18 pm   #25
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Default Re: Shaftesbury 519 amplifier

Hi Lawrence
How strange. Mine seems to have another 2 bolts on the front lip of the chassis. Am I missing anything?

Regards

Rob
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Old 12th Aug 2019, 7:22 pm   #26
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Default Re: Shaftesbury 519 amplifier

Are those nuts just front lip "clamp" nuts along with a couple of washers, if so the chassis should wiggle out without removing both of them.

Lawrence.
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Old 12th Aug 2019, 7:33 pm   #27
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Default Re: Shaftesbury 519 amplifier

You are a star. It’s exactly the same as yours as with a few tweaks it came out straight away. I’ve noticed that the speaker centre dust cap has been pushed in (more pics to follow).

Best regards

Rob
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Old 12th Aug 2019, 10:23 pm   #28
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Default Re: Shaftesbury 519 amplifier

Here are a few pics of the chassis, top circuit, inside of the speaker and speaker number.
Is the speaker suitable for use with an electric guitar? it appears to have a very tiny magnet for a 10" speaker?

Best Regards

Rob
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Old 12th Aug 2019, 11:25 pm   #29
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Default Re: Shaftesbury 519 amplifier

Not sure if you have found these web pages yet but there is some info on the amp here:-

http://www.vintagehofner.co.uk/britamps/restof.html

http://www.vintagehofner.co.uk/amps/shaft1.html

It looks like they were made early to mid sixties which seems to tie in with the date on the capacitor. Looking at the photos it looks like the speaker is original so I'm sure it will be fine - it seems to have lasted nearly 60 years so far! With a single EL84 it will only be about 5 watts, a lot of small guitar amps from that era used the commonly available radio speakers of the time.
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Old 13th Aug 2019, 7:26 am   #30
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Default Re: Shaftesbury 519 amplifier

If you are worried by the indentations on the central speaker dome/dustcover, these can usually be pulled out using sticky tape. Evenso, this is unlikely to have any noticable acoustic effect.
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Old 13th Aug 2019, 8:03 am   #31
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Default Re: Shaftesbury 519 amplifier

That speaker was almost certainly pushed in like that from the day it was fitted. They knew that no-one would ever see it. You know what I mean. Not a problem anyway.
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Old 16th Aug 2019, 4:49 pm   #32
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Default Re: Shaftesbury 519 amplifier

This may be a silly question- I’m ok to replace black Hunts with Mullard mustard caps.

Best regards
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Old 16th Aug 2019, 4:58 pm   #33
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Default Re: Shaftesbury 519 amplifier

Yes.
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Old 16th Aug 2019, 4:58 pm   #34
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Default Re: Shaftesbury 519 amplifier

Yes. They are better in almost every important way. But Mustards are not specifically better than ordinary modern polyester caps which will be fine too.

Don't chuck the Hunts until you've logged the date codes.
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Old 16th Aug 2019, 6:24 pm   #35
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Default Re: Shaftesbury 519 amplifier

Age old question, when to replace old out of value resistors? I’ve just measured an old 150k no tolerance marked, at 177k. I am aware that at this age it is possible to get away with wide tolerances but at what point should they be replaced?

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Old 16th Aug 2019, 7:11 pm   #36
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Default Re: Shaftesbury 519 amplifier

No tolerance mark are normally +/-20%.
So 177K is just in tolerance.
Replacement really depends on where in the circuit the resistor is.
If it is critical to the correct operation, is matched to another of similar value etc. or is likely to drift further out of spec under load (heat, voltage, noise, etc.).

Alan
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Old 16th Aug 2019, 8:04 pm   #37
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Default Re: Shaftesbury 519 amplifier

On vintage stuff I allow 20% tolerance on resistors unless there's a good reason to do otherwise. Doesn't make a jot of difference generally. It doesn't take long to check every resistor in a vintage circuit. It's best to refer to the schematic though as there will be a few instances of parallel paths to watch out for. In which case just snip one end of the resistor and re-solder it after checking. For that I use thin, tinned copper wire formed into a narrow tube around some tiny round nosed pliers and then slipped over the two wire ends to be (re)joined, and then fill the tube with solder thus reconnecting the resistor to where it was connected. It looks kinda OEM and works a treat. Better than trying to unsolder and unhook components from turret tags, valve bases etc. You always end up burning or overheating something doing that.
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Old 16th Aug 2019, 9:13 pm   #38
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Default Re: Shaftesbury 519 amplifier

Not good.....most so far are 50%+ out.

What is the orange component with the red band in post #29?
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Old 16th Aug 2019, 9:50 pm   #39
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Default Re: Shaftesbury 519 amplifier

Quote:
What is the orange component with the red band in post #29?
A resistor, looks like 3.3k +-10%...

Lawrence.
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Old 16th Aug 2019, 9:54 pm   #40
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Default Re: Shaftesbury 519 amplifier

I did try to measure it and was a bit confused with at reading of 56uf?.
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