GROUP BUY: Universal Audio 176 - a 100% faithful recreation of a legend! CLOSED!

[emrr]

A-19 is meant to handle DC current directly to a tube plate, at reduced low frequency response.  Not applicable here, low response should be better than spec with no DC as here.  Maybe not as good as A-18, maybe just as good, either way they used some of both. 

 

[Phrazemaster]

A-19 is meant to handle DC current directly to a tube plate, at reduced low frequency response.  Not applicable here, low response should be better than spec with no DC as here.  Maybe not as good as A-18, maybe just as good, either way they used some of both.

I appreciate that Doug. Sometimes EE talk sounds like Greek to me, but I'm slowly learning. So I gather from what you shared, both the A18 and the A19 were used in these units? With the A18 the preferred one, although it may or may not make a difference sonically?

Thanks - I see your posts over at GS sometimes and other places and I appreciate your wisdom.

In fact - all of you guys are amazing! Thanks to Martin (Rainton) for making this PTP possible, along with the rest of you geniuses and wannabes like me

 

[moltenwok]

Well that's all good-I found a nos pair of A18s  on eBay for $100 ea a while ago. So that leaves two of phrazemasters A19 up for grabs now that Doug has cleared that up. Thanks for your wise input..

 

[Phrazemaster]

A-19 is meant to handle DC current directly to a tube plate, at reduced low frequency response.  Not applicable here, low response should be better than spec with no DC as here.  Maybe not as good as A-18, maybe just as good, either way they used some of both.

By the way would the increased DCR of the A19 vs the A18 cause any issues?

Also to clarify, you said both the A18 and A19 were used in the 176, correct? References online said it was the A19, and one said both were used.

Thanks Doug!

Mike

 

[Phrazemaster]

Well that's all good-I found a nos pair of A18s  on eBay for $100 ea a while ago. So that leaves two of phrazemasters A19 up for grabs now that Doug has cleared that up. Thanks for your wise input..

Lucky! Jealous! Way to go!

 

[rainton]

Great info emrr!!
Thanks for sharing!

And sorry for the silence guys - I had so much work at the studio right now and the holiday season makes it very slow to finally get all quotes and infos I need to launch a possible run of 176 chassis kits.
But we're getting closer.

I'm on vacation now with my family until Sept. 14th and hope I'll have all info I need when I return.

In the meantime we could discuss some details. Many of you who are interested in the project want to use the API meter.
I actually planned to do the production run with a cutout for the SIFAM R32 meter - it's slightly larger than the API, but looks awesome, is very HQ and readily available.
HOWEVER I can do a special version for you guys with API cutout. But that would be ONLY for those who preorder a chassis kit, since I don't want to offer a kit later where people are struggling to find a certain vintage meter, you know what I mean?

Oh - and one more thing: I heard from a fellow forum member, that there might be a way to arrange a group buy for some vintage components such as UTC trannys, API meters, attenuators etc. for this build...we should here more about that soon

I'm still loving my prototype 176 and I'm afraid I need to build a 2nd one - damn it  ;D

 

[emrr]

The context of my ancient quote is that there was a point that no one wanted a UA compressor, and they sold for little/less than the various units with higher quality transformers, then once the UA company restarted they went up 10x in value on name recognition alone.  The minute before that they could be bought for $500-700 every day, then they were suddenly $7000 almost overnight.    Right before, you'd have had to trade (4) UA's for a BA-6, then they are suddenly worth more, for no sensible reason at all. 

If you are recreating something, you haven't done it unless you get the sound signature, which should mostly be the reason you would go to such trouble.  Which means as close to original transformers as you can get.  If it's the actual operating action of the device, you are then free to redesign with whatever you want, change large portions of the circuit, and call it whatever other than a UA 175/176 you want.  As well, it's not 'frequency response' exactly, as that may appear no different, but harmonic content among other minor things. 

 

[Quayhog]

What power transformer and choke set are the USA builders considering?  I can't find anything at Edcor and the Hammond site is hard to search.
The minimum requirements that I get from looking at the schematics are an X mount type.  200ct @ 100 ma, 6.3v @ 2a and 5v @ 2a..  A 225ct could be manageable.
The plate current requirements for the tubes, less GZ34 is 63 ma,  and the heaters consume 1.6 amps.

 

[beatnik]

Hammond 372X should be a good candidate and it has configurable primaries

 

[Quayhog]

I think that's the one I found that would  work.  When I bought the Sowter output transformer they recommended a 225ct at 100 ma.  I couldn't see where in the circuit that would require that much current. Almost double what I figure. 

We need to locate a source for the switched 25KL attack pot.  DP1T.

 

[beatnik]

urei schematics shows a 650V C.T. transformer and 295V on the output tube plates. the sowter transformer could probably work with some tweaking of the power supply resistors, but as you said this circuit doesn't need that much current

the attack pot is the same as the 1176 . you can get it from mouser

 

[kosi]

expensive version:
https://goo.gl/VXj8uf

 

[rainton]

What beatnik wrote regarding the attack pot.
Also available at Banzaimusic.com:

https://www.banzaimusic.com/Alpha-24-SPDT-25k-lin.html

The schematic calls for a DPST switch (which is exactly the one kosi posted the link to) - but the way it's wired you can also use an SPDT and the Alpha has a nice feel and does the job well!

Regarding the power transformer - I welcome the discussion

Following several 175b or 176 projects, they all used the Hammond 370BX - which is the same one as suggested for the Pultecs.
Drip Electronics recommends it for their 175b pcb version and another builder here successfully used it for his 176 build a couple of years ago.
I tried that transformer for my prototype and it works.
I have to admit though - I had the primaries wired up for 240V use first (even though we have mostly more like 220-230V here) and ended up being rather on the low side voltage wise. I rewired the primaries for 220V and am now still a little low but within 6% of specs - so that's not too bad

Even though I can say the transformer gets rather hot after a couple of hours of use. I'd say like 50°-55° celsius.

The problem is, space is at a premium at the back of the unit. On the right side (viewed from the back) we're completely depending on the pcbs, since many components that stick out the back are soldered straight to the pcbs. So the layout is predefined.
And to the left of the output transformer the space is extremely tight. I could try to get maybe 8-10mm more to mount a larger transformer but I'm not sure yet if it's possible.
The size of the 370BX make it fit perfectly.

Choke can either be Hammond 158M or Triad C-7X.

In terms of the "low budget" UTC iron: I think emrr's posts say it pretty well.

When I'm committing to the quest in recreating the iconic vintage gear I want to go for it's original signature sound. I want to find out what exactly it is why people love the sound of a particular unit.
That certain sound character was,  what I experienced many times in the past when I finished an authentic replication, instantly sounded familiar in some way - most likely due to having it heard on countless records?

What I can say in regards of the 176 - I used UTC-01 and UTC-A19 together with a Sowter output transformer - and my 176 indeed sounds very special compared to other pieces of gear I own - but in a very very pleasant way!! I love it
I'd love to do a shoot out with a vintage unit one day...

And YES - I will offer adapter plates

 

[core13]

Thank you Rainton for the precision

for USA poeple the pot can be found here

http://www.hairballaudio.com/catalog/parts-store/potentiometers/fet-compressor-attack-control

concerning the power tx, if it get hot and voltage are low  it's because it reach his limits curent wise and it isn't very good.
it can fail some day

does sowter power tx can do the job?

 

[beatnik]

I have to admit though - I had the primaries wired up for 240V use first (even though we have mostly more like 220-230V here) and ended up being rather on the low side voltage wise. I rewired the primaries for 220V and am now still a little low but within 6% of specs - so that's not too bad

in this case make sure filament voltages are still within correct ranges, if they too hot that might shorten tubes life.
with just 20V difference on the primary it should be fine, but it's better to double check this. in any case would be easy to drop the voltage with some resistors in series with the heaters

imho it would be better tweaking the power supply resistor R44 / 1,5K , since all the circuit gets powered off that node, it would be easy to adjust the resistor value to drop less voltage thus getting the optimal voltages at the plates.

i suggested the 372X because the ht voltage is a bit closer to what it's on the diagram. the currents for the ht and the 6.3 filament have also more margin, the 370BX is a bit closer to the limit

i know the 372X fits a 2U chassis mounted horizontally, because I used it in the past, but you will have to check with your chassis
imho I would go for a less authentic look on the back panel (which anyway nobody ever looks at) but having a power transformer that runs cool, even after more than two hours operation

 

[beatnik]

expensive version:
https://goo.gl/VXj8uf

that's not expensive, it's ridiculous

 

[core13]

i suggested the 372X because the ht voltage is a bit closer to what it's on the diagram. the currents for the ht and the 6.3 filament have also more margin, the 370BX is a bit closer to the limit

i know the 372X fits a 2U chassis mounted horizontally, because I used it in the past, but you will have to check with your chassis
imho I would go for a less authentic look on the back panel (which anyway nobody ever looks at) but having a power transformer that runs cool, even after more than two hours operation

aggree with that
the 370bx is sized X7 and the 372X is sized X8 so it's bigger
if we are sure it can fit I will go with this model also

 

[rainton]

I agree as well but the X8 size is 10mm wider - im not sure if that's possible.
And it's not just about authentic looks it's simply about space.

This thing is packed on the back.
We have two the GZ34 + the OB2 Tube + fuse holder to the left of the power tranny (even the cutout for the power cable is on the side of the unit because of that)

And to the right of the power tranny there's 2 can caps before the first pcb mounted Tube

I also found the 372x to be a better choice electronically but the one thing is I don't know if I can make it fit and the other thing is that - as mentioned by beatnik another option would be to change the values of the power supply resistor R44 (which I haven't done yet)

Anyway - in regards of the correct voltages - all measured voltages - even filaments are within 6% of specs

I'll see what can be done to make the 372X fit but can't promise yet.

Maybe we could talk to Gregory with Drip electronics - he suggests the 370BX for his 175b as well

I know a couple of people who built a Drip 175b but none of them had a power tranny failure yet...

 

[beatnik]

imho it would be better to sacrifice the obsolete capacitors in favour of a beefier power transformer, with a bit of headroom in terms of current supply, so it doesn't run hot. this is just my personal opinion and i am not an engineer, i don't know how long it takes to burn out a power transformer, so if you are sure the smaller transformer it's gonna be fine anyway, then ignore my comments

 

[kosi]

Difference between Hammond Sizes X7 / X8 is only 6,35 mm in length, width and height is the same

Hammond 372x is 82,55 mm
Hammond 370BX is 76,2 mm