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

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Old 8th Jul 2019, 12:27 pm   #21
dekor8tor
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Default Re: Hacker GP42 and AL42 restoration help

Thanks Brassbits I will have a look.
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Old 8th Jul 2019, 12:32 pm   #22
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Default Re: Hacker GP42 and AL42 restoration help

So does it buzz or hum with the volume control turned up or down or both?

See my post #20.
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Old 8th Jul 2019, 12:32 pm   #23
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Default Re: Hacker GP42 and AL42 restoration help

Thanks for that techman i do undetstand where you are coming from that is why i came on here to ask gor help and advice which is exactly what i have got
I am just taking Michaels advice on what he changes before he powers one of these amps after they have been standing for years i am not and dont want to rebuild the amps just change what normally needs changing
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Old 8th Jul 2019, 12:32 pm   #24
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Default Re: Hacker GP42 and AL42 restoration help

We haven't had any feedback (no pun intended) from the OP regarding the hum or buzz.
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Old 8th Jul 2019, 12:33 pm   #25
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Default Re: Hacker GP42 and AL42 restoration help

But you've already powered them up as you say there's a buzz.

And also taken all those voltage readings!
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Old 8th Jul 2019, 12:39 pm   #26
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Default Re: Hacker GP42 and AL42 restoration help

Hi Michael would you be able to send me a link for the resistors at rs please
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Old 8th Jul 2019, 12:41 pm   #27
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Default Re: Hacker GP42 and AL42 restoration help

The hum is there when you turn the volume up or down
Sorry for forgetting i am at work
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Old 8th Jul 2019, 12:47 pm   #28
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Default Re: Hacker GP42 and AL42 restoration help

The OP has stated that he only wants to change components which are faulty rather than doing a blanket change. A good idea in my opinion.

He has submitted voltage readings and my only comment about these is the differing voltages on the cathodes of the triode sections of the valves. The 2.2k cathode resistors may have changed value, as might the 220k anode resistors, something easily checked with a meter on resistance range. In fact a check on all resistors to find any which are out of tolerance would be a good idea.

Capacitors are harder to test, but a check to make sure there's no positive voltage on the control grids (pin 8) of the pentodes would be in order. A voltage here would indicate electrically leaky coupling caps C6 and C7.

I would also bear in mind Michael Maurice's knowledge based comments.
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Old 8th Jul 2019, 1:24 pm   #29
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Default Re: Hacker GP42 and AL42 restoration help

Hi Graham i have measured the voltage across r6 and r7 and got r6 87v and r7 128v also i measured the resistance of both resistors and got 280ohm from both i hope this helps many thanks
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Old 8th Jul 2019, 1:53 pm   #30
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Default Re: Hacker GP42 and AL42 restoration help

Very odd. Are we both singing from the same service sheet (R&TVS)? Those resistors should measure 220k (220,000 ohms).

EDIT. Colour code red, red, yellow.
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Old 8th Jul 2019, 1:54 pm   #31
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Default Re: Hacker GP42 and AL42 restoration help

Got called away by the phone.

I've not got the circuit in front of me, so can't verify your resistance readings, but you should know if you're getting the correct readings compared with what's listed in your service sheet.

So is 280 ohms correct - you tell me as you've got the circuit diagram in front of you?
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Old 8th Jul 2019, 2:01 pm   #32
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Default Re: Hacker GP42 and AL42 restoration help

Quote:
Originally Posted by dekor8tor View Post
The hum is there when you turn the volume up or down
Sorry for forgetting i am at work
It therefore sounds as though one or both of the smoothing capacitors may possibly be faulty and NOT all those other components you seem to want to change
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Old 8th Jul 2019, 2:08 pm   #33
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Default Re: Hacker GP42 and AL42 restoration help

There are 4 capacitors on the HT line 50+50uf reservoir and smoothing cap then the HT line is then RC decoupled by R15 1.5k/C16 16uf then R10 10k/ C8 8uf.

The smoothing resistor between the 50uf caps is 220ohm.
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Old 8th Jul 2019, 2:20 pm   #34
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Default Re: Hacker GP42 and AL42 restoration help

It's probably best that you carry on with your investigation of the fault when you've finished work and settled down at home with the actual unit in front of you.

As I say, I don't have service information for this player here in front of me, so my advice is general for players of this type. The reservoir and smoothing capacitors will be of the 'electrolytic' type and are quite likely to be combined inside a large round silver can with the values and voltage rating marked on the side. After the unit has been on for a few minutes, see if the silver can is feeling slightly warm to the touch. If it is, then this will indicate that it's electrically leaky and will need replacement. Don't run the unit for too long in this state as they can thermally run away, getting increasingly warm and are likely to go off with a bang if left with power applied for long enough!

Find out what components you ACTUALLY NEED before even thinking about putting in an order. I fully qualified as a radio, TV and electronics engineer (City & Guilds) over five years of day release at college in the early to mid 70s, so I "should" know what I'm talking about - others may disagree
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Old 8th Jul 2019, 2:58 pm   #35
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Default Re: Hacker GP42 and AL42 restoration help

Thanks all for your advice it is greatly appreciated and i understand what you are all saying so i will take techmans advice and wait until i have finished work and i am at home with the unit in front of me
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Old 8th Jul 2019, 3:10 pm   #36
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Default Re: Hacker GP42 and AL42 restoration help

I think thatís very good advise, far better for you to be able to concentrate and have the Amps etc in front of you.
Your getting excellent advice from the forum members, good luck.
Cheers
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Old 11th Jul 2019, 11:11 pm   #37
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Default Re: Hacker GP42 and AL42 restoration help

Good evening all i have had a chance to measure the voltages as stated in the service manual this is for the amp out of the GP42

HT1 C12 325V
HT2 C11 320V
HT3 C8 303V
V1A PIN 9 ANODE 199V
V2A PIN 9 ANODE 293V
V1B PIN 6 ANODE 320V
V2B PIN 6 ANODE 310V
V1A PIN 2 CATHODE 1.04V
V2A PIN 2 CATHODE 0V
V1B PIN 7 CATHODE 1.4V
V2B PIN 7 CATHODE 4.0V

They are out compared to the readings in the manual i hope someone can shed some light and point meinthe right direction
Many Thanks
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Old 12th Jul 2019, 12:50 am   #38
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Default Re: Hacker GP42 and AL42 restoration help

V1a/V2a anodes are high, this could be due to the meter you are using, a digital meter tend to give higher readings in circuits with high value resistors.

The cathode voltages are interesting, the pentode cathodes are low, cathode resistors or cathode bypass capcitors could be faulty.
You havent taken the screen grid G2 voltages pin 3 on both valves. If the G2 voltages are accepable and the cathode components are Ok then it points to low emmision ECL86 valves which will be ashame, they are expensive.

The cathode voltages on v2a is also incorrect, check the cathode components in that section, again it could be faulty ECL86.

Before sourcing valves check the components metioned and also may as well check the ones that Michael in post 15 if you have not already checked them.

Valve seem to be about £50 for a pair.
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Old 12th Jul 2019, 7:47 pm   #39
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Default Re: Hacker GP42 and AL42 restoration help

Good evening Frank i have just checked voltages on G3 both valves they both read 300v
Should i change the components as stated by Michael or are the valves gone
Many thanks
Also when the amp is powered up with no speaker connected there is a strange squealing noise coming from the amp

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Old 12th Jul 2019, 8:08 pm   #40
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Default Re: Hacker GP42 and AL42 restoration help

Quote:
Also when the amp is powered up with no speaker connected there is a strange squealing noise coming from the amp
Probably the output transformer protesting, don’t run it without a load of some kind, speaker, low value resistor.

Change those components, they will probably be out of specification, confirm the cathode components are good, they may be in that list from Michael to replace.

I am just wary of saying get two new valves at the price they are.
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