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

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Old 8th Sep 2019, 11:36 am   #121
Guitarist28
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Default Re: Shaftesbury 519 amplifier

As discussed, the nearest 3 watt resistor I had to 10k was 18k so I used this in series with a 1N4007 diode. This time it peaked at 309.4V and has taken quite some time to drop back to almost 0V once the power was switch off. It appears good to go I think.

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Old 8th Sep 2019, 12:35 pm   #122
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Default Re: Shaftesbury 519 amplifier

Looking good. Remove the diode and resistor then plug in just the rectifier valve and check that you get similar results.
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Old 8th Sep 2019, 6:30 pm   #123
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Default Re: Shaftesbury 519 amplifier

Ok, I have tried powering up with an EZ80 and recorded a steady 363V across the smoothing cap (425V surge rating). This is rated at 350V working but is it safe to assume a higher voltage given that there is no load i.e. the other valves not being in place?

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Old 8th Sep 2019, 8:36 pm   #124
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Default Re: Shaftesbury 519 amplifier

Time to try it in anger then.

I assume that the audio coupling capacitor connected to pin 2 of the EL84 has been changed?

When applying power be ready to switch off at the mains socket if anything untowards happens.

If you monitor the HT when powering up it should rise once the rectifier has warmed up, then fall as the other valves start drawing current.

If that's OK check that there's no, or very little, positive voltage on pin 2 of the EL84 measured wrt chassis.

If that's OK it's time to plug in a guitar and see if the amp works.
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Old 8th Sep 2019, 9:02 pm   #125
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Default Re: Shaftesbury 519 amplifier

Yes I have (see attached picture). If I put all the valves back in then I will need to load the output transformer so I suppose I could either temp rewire the speaker or use a large power resistor (i've several from about 4R upwards with large wattages).

I think it's also time to clean up the speaker baffle to put the new speaker grille cloth on.

I do hope that it's going to sound reasonable after all of this effort but I can only wait and see.
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Old 8th Sep 2019, 9:04 pm   #126
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Default Re: Shaftesbury 519 amplifier

Yes don't power it up without a load connected to the output transformer. Given that the speaker is internal to the amp I'd assumed that was the case.
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Old 10th Sep 2019, 7:20 pm   #127
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Default Re: Shaftesbury 519 amplifier

All valves in but as it's my workshop I only tried with a guitar lead connected (no guitar). I've powered on and there is very little hum and with my fingers earthing the end jack plug it's definitely working. However, maybe its just me, it was at full volume and didn't appear to have much gain at all.
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Old 10th Sep 2019, 7:59 pm   #128
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Default Re: Shaftesbury 519 amplifier

Best try it with a guitar then.

If no joy let's have some voltage readings.

Heater voltage on load. AC Volts with meter across heater pins.

HT at smoothing capacitor. DC wrt chassis.

All pins of output and driver valves except the heaters. DC wrt chassis.
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Old 10th Sep 2019, 8:01 pm   #129
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Default Re: Shaftesbury 519 amplifier

Agreed. I did measure the voltage at the smoothing cap as you recommended..... 287v.
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Old 10th Sep 2019, 8:06 pm   #130
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Default Re: Shaftesbury 519 amplifier

OK. If you let us have some voltage readings for the valves we'll be able to tell whether they're drawing anode/screen current and whether the bias is correct.

What is the driver valve? I don't recollect seeing it mentioned. Only EZ80 and EL84.
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Old 10th Sep 2019, 8:16 pm   #131
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Default Re: Shaftesbury 519 amplifier

Ecc83 with an EF86.
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Old 11th Sep 2019, 10:53 am   #132
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Default Re: Shaftesbury 519 amplifier

Ok measured the ECC83 and EL84 using a Uni-T UT61E to ground
ECC83
Pin 1 = 101V DC anode (1)
Pin 3 = 0.9V cathode (1)
Pin 5 = 3.3V AC heater
Pin 6 = 99V DC anode (2)
Pin 7 = 1.28V AC grid (2)
Pin 8 = 0.8V (cathode (2)

EL84
Pin 2 = 260V AC Control grid.
Pin 3 = 285V DC Cathode suppressor grid
Pin 4 = 3.2V AC Heater
Pin 5 = 3.2V AC Heater
Pin 7 = 259V AC Anode

I’m not sure if these are what would be expected?

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Last edited by Station X; 11th Sep 2019 at 11:35 am. Reason: Electrode designations added.
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Old 11th Sep 2019, 11:39 am   #133
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Default Re: Shaftesbury 519 amplifier

Something seriously wrong there. There should be no AC voltages present apart from on pins 4 and 5, the heaters, which look OK assuming a centre tapped heater supply.

Apart from that I think you're numbering the pins the wrong way. Looking from UNDER the chassis the pins number clockwise from the gap or spigot.

I'll reverse the pin order for the EL84 and see if it makes any sense.
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Old 11th Sep 2019, 11:50 am   #134
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Default Re: Shaftesbury 519 amplifier

I've reversed the EL84 pin order and it makes some sort of sense. Lest I lead you up the garden path I think it would be best if you took a new set of readings and confirmed that you're numbering the pins correctly.

EDIT. I note that some pins are missing from your list. Some of these will be internal connections (ic), but pin 9 (screen grid) of the EL84 is important.
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Old 11th Sep 2019, 11:53 am   #135
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Default Re: Shaftesbury 519 amplifier

Ok, I will retry.
Perhaps it's me. I will retry with another multimeter on DC only.
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Old 11th Sep 2019, 4:55 pm   #136
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Default Re: Shaftesbury 519 amplifier

I've attached what I am seeing and measuring as the pin outs for the EL84 valve. Pins 4 & 5 must be the heaters as pin 6 has no connection. Again, with the connection to ground, the measurements are as follows:
pin 2 = 0.0025v
pin 3 = 0V
pin 4 = 1.3V AC
Pin 5 = 1.3V AC
pin 7 = 276V
pin 8 - n/c
pin 9 = 251V

I believe that the heater voltages appear low.

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Old 11th Sep 2019, 5:06 pm   #137
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Default Re: Shaftesbury 519 amplifier

You need to measure between pins 4&5 for the AC heater voltage, not WRT chassis.

Lawrence.
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Old 11th Sep 2019, 5:11 pm   #138
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Default Re: Shaftesbury 519 amplifier

Has this amplifier got a hum bucker( virtual centre tap) for the heaters? This usually consists of a resistor( often 100 ohms) connected from each side of the heater winding to chassis- so the junction of the two resistors is at chassis, sometimes at the pilot light if you have one. That might explain the 3.3 volts or so from each heater pin to chassis. You obviously have heater volts because the EZ80 is providing good HT.
Measure heaters between pins 4&5( ac of course) on the EL84 and I bet it will be as expected. The ECC83 has the facility to run the heaters at 12 volts( in series pins 4-5) or parallel for 6 volts 4&5 linked to one side of the heater supply and pin 9 to the other. So you might see 6 volts across 4/5 & 9. All the valves you have number the same way, as previously explained.

Your latest readings indicate you have no cathode voltage on the EL84 ( pin 3). This could be a faulty valve( or socket/ wiring fault/error) or the cathode resistor is open circuit, but I would expect to see something as there would be a path through the meter, or a short circuit cathode bypass capacitor, again unlikely as there is good HT and the EL84 isn’t glowing red hot!
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Last edited by Tim; 11th Sep 2019 at 5:33 pm.
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Old 11th Sep 2019, 5:11 pm   #139
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Default Re: Shaftesbury 519 amplifier

Thank you.... 6.5v.
I must be getting old, 60 today!!
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Old 11th Sep 2019, 5:13 pm   #140
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Default Re: Shaftesbury 519 amplifier

As you say heater voltages are low, but this is a change from previous posts where you I think saw around 7.5V across the heaters ie between pins 4 and 5?

Zero volts on pin 3 the cathode may indicate that the valve is passing no anode or screen current, but that depends on the bias arrangements. If auto-bias is used with a resistor from cathode to ground I'd expect to see a voltage across it.

Please confirm the bias arrangements.

EDIT. Posts crossed. Ignore first sentence.
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