Tubelab SPP first timer build

[Steve Morley]

This one from Primary windings for power: https://primarywindings.com/product/mains-transformer-mullard-5-10-stereo/ Unfortunately Primary Windings doesn't have a suitable choke.

See attached parts list. Since it was compiled some of the resistors are only available from Mouser in huge quantities. You'll have to take a troll through the Mouser search functions for similar in small quan. The trim rings for the tube holes are in parts list too.

HiFi collective in the UK might be a source for parts not available from Mouser. https://www.hificollective.co.uk/

I just left C101 out and the amp works OK.

S.

 

[calpe]

To determine the value of C101 you need a square wave generator with about 10kHz.
You have to look at the result with an oscilloscope.
The value will be between 100pF to 800pF.

You can also determine the value with your ears.
Look here:
https://www.diyaudio.com/community/...ensation-capacitor-on-the-tubelab-spp.201612/
https://www.diyaudio.com/community/threads/tubelab-simple-p-p.148694/post-6492730

Thanks stonegreen
The first link George (Tubelab) tells us...

Yes. The capacitor is used to tweak the feedback compensation for the high frequencies. The usual way to do this is to apply a 10 KHz square wave to the amp with a resistive dummy load attached and tweak the cap value for the best square wave with a scope.

Most builders do not have a scope, or a good square wave generator. So the next best thing is to use your ears and tune for the best sounding highs with your speakers. After all you don't run the amp with square waves and dummy loads. I have seen values from 270 pF to 880 pF work the best using the scope and square wave method. The value depends on the OPT being used. It you must guess, start with 470 pF. That is probably better than no cap.

 

[calpe]

This one from Primary windings for power: https://primarywindings.com/product/mains-transformer-mullard-5-10-stereo/ Unfortunately Primary Windings doesn't have a suitable choke.

I just left C101 out and the amp works OK.

That's the Tx i was looking at.
But Primary Winding gives these spec., that fall short of what George states in the Tubelab write up.
600V 200mA with Centre Tap (CT); 6.3V 4A; 6.3V/5V 2A
I've emailed Primary Windings.

Tubelab says to use a Tx with these spec.: -
300-0-300 VAC minimum 175mA; Rectifier filament 5 VAC 3 amps (using a 5AR4 valve).
Main filament - 6.3 VAC 4 amps.

As for C101 i'll get a couple of values and tune in my old ear, though as you've said, you left it out with no problems.

 

[Steve Morley]

A 5AR4/GZ34 draws 1.9 amps so the 6.3 winding that's tapped at 5 volts and supplies 2 amps is fine. The other two windings have sufficient current.

S.

 

[calpe]

Steve, I'm a bit anxious that there is only 100mA to the max. amperage that the Tx can supply.
Might be pushing it close to its limits and cause that winding to run too warm?

 

[mkane77g]

Watching this I have an SPP board that needs populating.

 

[Steve Morley]

calpe,

You'll be under on the other two windings as well so I wouldn't sweat it. The power trans will likely run a bit warm anyway. The PT in my ARC amp runs warm and it's over ten years old and still going. A PT in an amp from the 1960s runs quite hot and it's over 50 years old. Unless you are going to run your amp 24 hours a day every day it will live. If you really want overkill, at a cost, get a Hammond 372JX. It has about twice the required current on every winding.

mkane,

Welcome a-board (groan permitted). Check out this thread too: https://www.diyaudio.com/community/threads/easy-diy-tube-amp.384618/page-9#post-7054121

If you are in the USA, Edcor has a decent transformer set for this amp at a reasonable price if you don't mind waiting (they only build to order and it might take anywhere between 4 to 12 weeks. https://edcorusa.com/

Cheers, S.

 

[stephe]

calpe,

It has about twice the required current on every winding.

Cheers, S.

Do be careful of over spec'ing the heater windings. They come down to 6.3V at the rated loading, and lets say you have 3A of load and a 6.3V winding rated at 6A, you can end up with the heater voltage at 7V+

 

[Steve Morley]

On one of my SPP builds using a Hammond 272 JX, I wound up using the 125 volt primary tap, When up and running, the 6.3 and 5 volt taps were just about dead-on the nominal voltage. This was with a line voltage ~120 volts. It ran very cool, lower than most Hammond trannies.

Just another data point those considering a SPP build.

S.

 

[mkane77g]

Off topic a bit but, looking at Tx is one better than the other?

Hammond 372hx

Edcor XPWR131

 

[Steve Morley]

mkane,

The Edcor XPWR131 would result in a too high B+ for a SPP. Something like the XPWR008 would be better.

If you don't need 240 volt primary (300 series), the Hammond 272HX would be a little less money. The Hammond has a bit more secondary current than the Edcor XPWR008. But the Edcor would likely be fine for a SPP. The choice of XPWR008 versus 272HX might come down to price (Edcor $106, Hammond $136 at Antique Electronics) and availability, (Edcor 1 to 2 months, Hammond ??).

S.

 

[Steve Morley]

For OPTs the Hammond 1650FA is $142 ea. at Antique Electronics. The Edcor CXPP25-7.6K - 25W with 4, 8 & 16 ohm secondary is $102 ea., 1 to 2 month delivery.

I can't vouch for their OPTs but have had good luck with their power trannies, try Antek toroids. The price is right at $72 ea. https://www.antekinc.com/mp-25w76-25w-output-transformer/

S.

 

[mkane77g]

Thanks. Looking through my old notes I have CXPP257.6K marked and XPWR008. I'll get on it.

 

[calpe]

Much appreciate all the valuable views, thanks
We know that George (Tubelabs) tells us: -

I used 600 VCT (300-0-300) Hammond transformers in my amps and I get the correct voltage. This winding MUST have a center tap.
The rectifier filament winding should be 5 VAC at at least 2 amps. If a 5U4 or 5AR4 rectifier is used this winding must be at least 3 amps.
The main filament winding should be 6.3 VAC at at least 4 amps.

Playing it safely, sadly Primary Winding Tx (600V @200mA CT - 6.3V @4A and 6.3V/5V @ 2A does fall short.
So it's either a Tx from https://edcorusa.com/ :-
XPWR066 - [email protected] CT, [email protected], & [email protected] = Sale price$108.86, shipping extra
XPWR172 - [email protected] CT, [email protected], & [email protected] = $112.70, shipping extra
XPWR284 - [email protected] CT, [email protected] CT, & [email protected] = $118.89, shipping extra

or obtain a Hammond 372HX 600V, 6.3V, 5V - 230mA, 6A, 3A = £135~

I've already put my name down for overtime £££££££

 

[calpe]

Do be careful of over spec'ing the heater windings. They come down to 6.3V at the rated loading, and lets say you have 3A of load and a 6.3V winding rated at 6A, you can end up with the heater voltage at 7V+

Thank you kindly Stephe for your views.
I love your YouTube videos and those on the Monoblock too, you make it look so easy!

 

[jcalvarez]

Much appreciate all the valuable views, thanks
We know that George (Tubelabs) tells us: -

Playing it safely, sadly Primary Winding Tx (600V @200mA CT - 6.3V @4A and 6.3V/5V @ 2A does fall short.
So it's either a Tx from https://edcorusa.com/ :-
XPWR066 - [email protected] CT, [email protected], & [email protected] = Sale price$108.86, shipping extra
XPWR172 - [email protected] CT, [email protected], & [email protected] = $112.70, shipping extra
XPWR284 - [email protected] CT, [email protected] CT, & [email protected] = $118.89, shipping extra

or obtain a Hammond 372HX 600V, 6.3V, 5V - 230mA, 6A, 3A = £135~

I've already put my name down for overtime £££££££

I think the Hammond price you got is without VAT, right?

 

[calpe]

I think the Hammond price you got is without VAT, right?

Yep, that's right, as i hope not to pay U.K. VAT, that doesn't apply where i live, we though have to pay import duty.
I'm looking around for other suppliers, but of course i need to be careful ordering from too many places, shipping costs etc.
https://edcorusa.com/pages/don-audio do not ship to U.K. nor Europe, so it's down to https://www.don-audio.com/ (Germany) or other known reliable suppliers.
Suggestions anyone?

 

[Steve Morley]

calpe,

I had a look at Don audio and the CXPP25-MS-8K looks like a good choice and it's on sale!

See if Don audio has an Edcor XPWR066 power trans. That would work for you.

I still say the Primary Windings power trans would work just fine even though the 5 volt tap is rated at 2 amps. I've used many 2 amp rated trannies with GZ34s without problems.

S.

 

[Tubelab_com]

I still say the Primary Windings power trans would work just fine even though the 5 volt tap is rated at 2 amps. I've used many 2 amp rated trannies with GZ34s without problems.

The rated heater current for a GE 5AR4 or a Mullard GZ34 is 1.9 amps so a 2 amp 5 volt winding will work fine and is what I use with a Sylvania 5AR4 in my 20 year old TSE. I don't know where the 3 amp number comes from. It probably came from a misplaced copy and paste during the time when the web site was hacked and the backup was lost back in about 2009. That's why there are limited full build instructions for the SPP board. Use of a 5U4 or a 5R4 (not 5AR4) WILL require a 3 amp winding.

 

[calpe]

calpe,

I had a look at Don audio and the CXPP25-MS-8K looks like a good choice and it's on sale!

See if Don audio has an Edcor XPWR066 power trans. That would work for you.

I still say the Primary Windings power trans would work just fine even though the 5 volt tap is rated at 2 amps. I've used many 2 amp rated trannies with GZ34s without problems.

S.

Thanks again Steve.
I have been looking around with the little time i get...... very slowly advancing.....
It's hard earnt cash, so i don't want errors
Found these: -
https://primarywindings.com/product/25w-7600-ohms-ultra-linear-push-pull-output-transformer/ = Excl VAT £81.61, weight 2Kg
Shipping to Europe, they use Parcelforce Euro Economy, cost is very approx. via Globalvalue £30.90 (very expensive, but i'm checking with them).

https://www.don-audio.com/navi.php?...ad6ea9720a51a5f22&suchausdruck=CXPP25-MS-7.6K = £78,26 excl. vat)
Don-Audio - Shipping weight 2,70 kg. EU up to 5 kg 14,95; up to 10 kg 21.00.

To be able to order a Mains Transformer, could we know what is the correct rectifier valve in position V104?
A GE 5AR4, a Mullard GZ34, a 5U4 or a 5R4 valve?
Shame for new builders there are limited full build instructions, it doesn't make things easy.