Hacker GP42 and AL42 restoration help
 

Good afternoon everyone. I have decided to restore the two amps in the 41 and 42 and I would like to ask for your help from all of the knowledgeable people on this forum
I have read lots of forum posts regarding these amplifiers and with that knowledge I set about taking some readings and i would like some help in interpreting them please.

Thank you.

All of the readings are voltage.

R15 52.3v
R10 6.2v
R14 4.95v
R13 7.4v
R8 1.3v
R16. 0v
R5. 0v
R4. 0.85v
R21. 10.7v
R18. 0.01v
R19. 0.01v

C3. 0.87v
C5. 1.3v
C9. 7.3v
C10. 7.5v
C8. 236v
C16. 253v
C7. 137v
C6. 136v
C14. 0v

I hope some one can help me as I don't want to go changing things that don't need changing these readings are from the AL41.

Many thanks.

Re: Hacker GP42 and AL42 restoration help
 

You don't specify with respect to what or whether any of them are AC...

Valve electrode voltage measurements (voltages on the valve pins with respect to chassis) are the best ones to post up, keeping in mind that the valve heaters are AC fed.

Lawrence.

Re: Hacker GP42 and AL42 restoration help
 

The readings you have are ambiguous, were they taken across the component, one side to chassis (which side) etc?

Best thing is to get the manual and use the voltages in that, also if there any Supamold capacitors you will probably find they are faulty, replace the ones connected to the control grids of the output pentodes.

Crossed with Lawrence.

Re: Hacker GP42 and AL42 restoration help
 

In addition to the two previous posts I wonder if the two amps actually work? It would be useful to know that.
Cheers
John

Re: Hacker GP42 and AL42 restoration help
 

It is also a good idea to state which service information you are using and hence what the component numbers refer to.

Mike

Re: Hacker GP42 and AL42 restoration help
 

Hi thanks for that i will post the voltages against the ones in the manual that i downloade from here all the voltages are dc
Many thanks

Re: Hacker GP42 and AL42 restoration help
 

Please note what the first two posts asked, this is important to fully understand your voltage readings.
Cheers
John

Re: Hacker GP42 and AL42 restoration help
 

hi all i have measured dc voltage as mentioned in the service manual as follows

H.T.1 C12 280vdc
H.T.2 C11 264vdc
H.T.3 C8 237vdc
V1a pin 9 anode 150vdc
V2a pin 9 anode 167vdc
V1b pin 6 anode 258vdc
V2b pin 6 anode 260vdc
V1a pin 2 cathode 0.8vdc
V2a pin 2 cathode 1.3vdc
V1b pin cathode 7.3vdc
V2b pin 7 cathode 7.4vdc

R15 52.3v
R10 6.2v
R14 4.95v
R13 7.4v these are resistor voltages across the resistors dc
R8 1.3v
R16. 0v
R5. 0v
R4. 0.85v
R21. 10.7v
R18. 0.01v
R19. 0.01v

C3. 0.87v
C5. 1.3v
C9. 7.3v
C10. 7.5v
C8. 236v these are capacitor voltages across the capacitor dc
C16. 253v
C7. 137v
C6. 136v
C14. 0v


i hope these make sense to someone because if any components have failed i would like to change them before i use the equipment
many thanks for you help

https://www.vintage-radio.net/forum/...d.php?t=111739

Re: Hacker GP42 and AL42 restoration help
 

this was the thread i was following to get my voltage readings

https://www.vintage-radio.net/forum/...d.php?t=111739

Re: Hacker GP42 and AL42 restoration help
 

The voltages are not that far out, I have not taken note of the voltages across the resistors and capacitors only the ones from the manual.
Check C6 and C7, those being faulty can cause damage, the other slight differences in the voltages will be small changes in the value of some resistors and degraded emission in the valves but they are not that bad.

Has John asked do the amplifiers work and if so how well?

If C6 and C7 are good and the amplifier works well I would leave it as it is.

See what other opinions are.

Re: Hacker GP42 and AL42 restoration help
 

Good morning Frank thanks for that yes both amplifiers work i was just making sure there were no problems as i do get a buzzing sound from both
Looking at the amps c6 and c7 both look like mustard mullards
How do i check the secondary voltage thanks and heater to V3 and V1 i dont know the pin layout on that valve it doesnt show that in the manual
Many thanks

Re: Hacker GP42 and AL42 restoration help
 

The three valves all have their heater connection on pins 4 and 5, the ECL86 have two valves in each envelope, triode and pentode, their heaters are connected to pins 4 and 5. Your meter on AC volts 10v or similar setting depending on what ranges your meter as and test across pins 4 and 5 on all three valves.
The rectifier V3 is the same but it has its own heater winding on the trannsforner.

The “secondaries “ this is the supply to the anodes of the rectifier, meter set to AC volts range 1000v. One meter lead to chassis the other taking separate readings on pins 1 and 7, both should be in the range of 250VAC.

I will be surprised if there is much wrong with them.

Need more information on the buzzing.

Re: Hacker GP42 and AL42 restoration help
 

The heater pins on all B9A base valves are pins 4 & 5. Viewed from underneath, count clockwise from the gap. Nominal heater voltage is 6.3VAC. measured across the pins i.e., between pin 4 & pin 5. The secondary voltages (also AC) are measured across the Transformer windings. In the case of the HT secondary, the voltage can be measured between earth and each end of the winding, although, as the HT DC voltages are reasonable, there is no real need to measure the HT secondary voltage at the transformer. Likewise, if the voltage at the heater pins of each valve is approx. 6.3VAC, there is no need to measure that at the transformer. (Edit; cross-posted with Frank (Nuvistor)

Re: Hacker GP42 and AL42 restoration help
 

I presume you mean a “buzzing sound” when you touch the input terminals, relatively silent otherwise?
Cheers
John

Re: Hacker GP42 and AL42 restoration help
 

Whenever I service these amplifiers, I replace the following on sight before powering up:

The two 220K anode load resistors on the top tag strip.

The two 820K and 1M resistor around the valve holders.

The two 2K2 and 220R resistors on the bottom tag strip.

The for 47uF capacitors on the bottom tag strip

The two mustard capacitors are almost always OK.

Re: Hacker GP42 and AL42 restoration help
 

Good morning Michael thankyou for tha information it is greatly appreciated Can you point me in the right direction as to where to buy these components from please
Many thanks

Re: Hacker GP42 and AL42 restoration help
 

I find radio spares a good source for parts

Re: Hacker GP42 and AL42 restoration help
 

That's RS Components nowadays- unless you're also a bit vintage ;D

(Rebranded in 1971)

Re: Hacker GP42 and AL42 restoration help
 

I use Vishay 2W Metal resistors available from RS. They are rated at 500V, modern carbon films are not rated for high voltage.

I also use Vishay axial capacitors.

Re: Hacker GP42 and AL42 restoration help
 

Even after you've changed all the components mentioned above, you'll still have the 'buzzing', as none of the ones mentioned will be the cause of that!

It's absolutely no good whatsoever just jumping in and replacing components randomly without actually knowing why you're changing them and whether they're actually faulty in the first place, as it's been proven many times on here that it'll only lead to disaster!

Proper fault finding and an analytical and logical approach is what's needed. Firstly, the buzzing sound, is it a buzzing sound or is it more of a hum?

Is this 'buzz' or hum regardless of volume setting, ie, does it disappear when the volume control is turned right down to minimum?

It's possible you may have a bad signal ground problem at amplifier input stage, or if the 'hum' is there regardless of volume control then you could have a problem with one of the smoothing capacitors, but you MUST do proper fault finding!!

Re: Hacker GP42 and AL42 restoration help
 

Thanks Brassbits I will have a look.

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.

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

Re: Hacker GP42 and AL42 restoration help
 

We haven't had any feedback (no pun intended) from the OP regarding the hum or buzz.

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!

Re: Hacker GP42 and AL42 restoration help
 

Hi Michael would you be able to send me a link for the resistors at rs please

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

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.

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

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.

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?

Re: Hacker GP42 and AL42 restoration help
 

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;):)

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.

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;D

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

Re: Hacker GP42 and AL42 restoration help
 

I think that’s 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
John

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

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.

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

Re: Hacker GP42 and AL42 restoration help
 

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.

Re: Hacker GP42 and AL42 restoration help
 

Ok Frank i will change what Michael advises and do a re check
Many thanks

Re: Hacker GP42 and AL42 restoration help
 

If you still have voltages that are a long way out after replacements are fitted. You could measure the cathode voltages of the pentodes, they are 1.4v and 4v at present. Swop the valves over, if the low voltages follow the valve then it’s a sign that the valves are low emission.

Re: Hacker GP42 and AL42 restoration help
 

Hi Frank connected speaker and plug for stylus and checked voltages again this is what i got compared to last readings

HT1 C12 286V
HT2 C11 272V
HT3 C8 248V
V1A PIN9 164V
V2A PIN9 120V
V1B PIN6 265V
V2B PIN6 265V
V1A PIN2 0V
V2A PIN2 0V
V1B PIN 7 7.1V
V2B PIN7 7.2V

Re: Hacker GP42 and AL42 restoration help
 

Voltages G3 = 257v on both

Re: Hacker GP42 and AL42 restoration help
 

Those look more like they should do, have you changed any components but I would have expected pin 2 to have about 1v on them. The Pentode cathodes are about right so the emission is ok.

Re: Hacker GP42 and AL42 restoration help
 

No all i have done is connect the speaker

Re: Hacker GP42 and AL42 restoration help
 

So the voltages you took before were without the speaker or dummy load?

Re: Hacker GP42 and AL42 restoration help
 

Yes

Re: Hacker GP42 and AL42 restoration help
 

Oh well you will know for the future, the amplifier was probably going unstable.

So back to the problem, check those components that Micheal suggested.

Re: Hacker GP42 and AL42 restoration help
 

Ok thanks will do