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Old 5th Jan 2015, 6:47 pm   #1
_Clint_
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Default Quad II TCC Block Capacitor Replacements

Happy new year everyone

I thought some of you may be interested in one guys obsession with the word ‘why’ I have always been inquisitive but now with time on my hands I sometimes wonder if I am not quite sane, so forgive me if this post seems to ramble, but I guess I am looking for acceptance in a mad house.

This brings me swiftly to my most recent ‘why’

I have been restoring some Quad 2 amplifiers and have been asked to do more, one of the things often discussed is the replacement of the TCC Block Capacitor used to smooth the HV line.

I have been experimenting and trying to understand exactly what is right or wrong here and why as there seems to be so many opinions over the internet.

One view I read a lot is that the GZ32 has a max C1 rating of 60uF (as per the data sheet) so you can fit any value up to this and your ok - (mostly I see 50+50uF retrofitted) - this is wrong as at 60uF it assumes a 150R Transformer winding resistance (Rt). Once translated the data sheet seems to show the following:

Maximum C - Transformer R
60uF - 150R
32uF - 100R
16uF - 50R

Interestingly the Quads Transformer Rt in the UK is 67R, which if you interpolate between the quoted 50 and 100R Sizes of C it sits at 22uF.

I am sure that rectifiers having an efficiency map not just min and max limits and here is why:

I have today been playing with 2 valve Manufacturers versions of the GZ32:
Brimar GZ32
Mullard GZ32

and 4 Electrolytic's

Original TCC Black capacitor measure for C and ESR to ensure its serviceable.
22uF 450v from the Panasonic EE range
33uF 450v from the Panasonic EE range
47uF 450v from the Panasonic EE range

My results are as follows:

>The Mullard runs hotter than the Brimar on all tests.

>The Mullard runs the coldest with the 22uF - The data sheet would suggest this valve and I think the reason it was not used in the quad was simply that it was not available, the 16uF was the max TCC did in that series. I have only seen a catalogue listing 4,8 and 16.

>The Brimar runs the Coldest with the 32uF, I repeated this test to make sure.

The valves run at almost the same temperature with the original TCC Block and the Panasonic's 22uF - probably a function of ESR - I have ordered some 16uF Panasonic's and will retest and report back if the reading is lower still for the Mullard.

Interestingly all the EE capacitors run at very close temperatures ~42C I put this down to surface area and increasing Ripple Rating, their max rating is 105C so these handle the job superbly.

I have seen a lot of people using up to 68uF here saying it makes no difference, but it does, with the original Mullard GZ32 its out of its comfort zone at 47uF in the Quad.

The Ripple Voltage on the GZ32 side halved 32V opposed to 64V and the RMS voltage (356V) DROPPED by 4V when the capacitance doubled from 16 to 32uF, the ripple after the choke on the pi filter with 16+16 uF at the KT66 anode was 1v

With 32uF and 16uF it was 860mV and with 32 + 32uF 850mV

So I currently have the following assumptions:

Rectifiers have efficiency maps and if you get this correct you will not only see better performance you can extend the life of the valve.

The Brimar GZ32 Valve (Newer construction) is more efficient that the older Mullard GZ32 type. (and being bottle shaped still looks correct)

The Newer Capacitors are more valve friendly - the 22uF Panasonic ran the Brimar colder than the original 16uF- to Be Confirmed when I have the Panasonic 16uF’s here.

The Maximum C on the GZ side should absolutely not exceed 32uF with either valve.

The capacitance on the other side of the choke does not make much difference so 32uF is fine here.



Open to comments and suggestions and corrections
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Old 5th Jan 2015, 10:49 pm   #2
GrimJosef
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Default Re: Quad II TCC Block Capacitor Replacements

A few comments I'd add:

The performance of the Mullard GZ32 will depend not only on that particular valve's history (I'm assuming it wasn't new out of a box) but also on when it was made. The practice at Mullard seems to have been steadily to improve their valves without changing the type number. So an early production GZ32 may well have started life poorer than a late production one. They did sometimes issue fresh data sheets though, with the improved performance shown in them.

Can I ask how you were measuring the DC and ripple voltages ? It's best to do it with a scope since then you can see what's really going on. Measurements of DC in the presence of a lot of AC can be a bit iffy if you're just using a multimeter, as can measurements of AC when the waveform is far from sinusoidal (which it is, obviously, for the ripple across a smoothing capacitor).

As far as the DC HT goes it's also worth keeping a close eye on the mains voltage. If it's not stabilised then fluctuations in it can easily cause the HT to vary by several volts.

Assuming the amp is running under quiescent conditions (no audio signal) and that we're not close to any resonances in the pi filter then the ripple after the choke should fall in inverse proportion to the smoothing (second) capacitor size. 32uF isn't a bad value but the ripple level, and therefore the audio hum level, will drop further if you make the capacitor larger.

Cheers,

GJ
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Old 5th Jan 2015, 11:27 pm   #3
dawaterfall
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Default Re: Quad II TCC Block Capacitor Replacements

There is a third option. With the original TCC block removed there is just enough space to fit 2 16uF AMPOHM polypropylenes (and another single 16 under the output transformer). With all components matched there is no hum. I'm using GEC U52 rectifiers and the whole amplifier is cooler running than stock. Yes, the B+ is a few volts down on a GZ32 but if the preamp + tuners are not being used the driver section is about on original spec.
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Old 6th Jan 2015, 12:22 am   #4
_Clint_
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Default Re: Quad II TCC Block Capacitor Replacements

Thanks for the input guys.

GJ: Do you have any of the Mullard datasheets? I only have a Philips one at my disposal.

All the valves were apparently unused, the Mullards were white boxed however they do not differ much from the low use one I have from an amp pull, the Brimars were retail boxed and I have 2 of each but both brought at the same time and assume same datecode.

Mains voltage was kept stable, measurements captured with a scope, see attached pictures.

I have tried to be as scientific as I can.

dawaterfall: all good options but I am more interested in keeping the amp looking very near standard, as such I am after some more TCC block caps to replace missing ones I have
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Old 6th Jan 2015, 1:09 am   #5
GrimJosef
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Default Re: Quad II TCC Block Capacitor Replacements

Well Philips and Mullard were the same company of course, but it's true that the commonly available Philips GZ32 datasheet contains only the 1949 curves. I have a couple of other versions both headed Mullard (one described as 'Issue 2 GZ32 953-1' from the loose-leaf Mullard Technical Handbook and one undated in the back of the little 'Mullard 5 Valve 10 Watt High Quality Amplifier Circuit' book http://www.priory-antiques.co.uk/ind...roductId=10909). But they don't contain any new data, just the old 1949 curves re-plotted on new graph paper. That doesn't mean the actual Philips/Mullard GZ32 valves didn't change with time though. I've got older and newer ones and they look quite different inside.

Cheers,

GJ
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