One more front.


Potato Cakes

So I had an interesting thing happen. Or perhaps unexpected would be more accurate. One of my 176 builds I used to do a record. Then when I received my matched 6BC8 tubes from Bowie, I did more testing, but then at some point of listening back through it, the input gain dropped. I messed around in the back of the rack and apparently the In+ connection was intermittent the whole time, so I fixed that but then I still had about a 10dB difference to the other unit. What it came down to is that the O-1 went bad, something I'm not sure how it happened since it had been working great this whole time. I have had transformers be faulty when purchased new, but never seen one go bad over time. Fortunately I have a pair of O-2 that I thought about selling but never did and after installing it everything is back to normal. Very strange but glad it was a fairly easy fix.

Thanks!

Paul

Potato Cakes

Here's both units up and running testing with some program material. I can't tell a difference with the controls set the same.

Thanks!

Paul

Phrazemaster

Hey Paul - great job in figuring that out! Thanks for sharing.

Mike
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Phrazemaster

This thread is starting to sound like an echo chamber...isn't anyone else building or gathering parts?

I was also wondering what folks are using for C3 and C4. In Martin's pix it looks like he used tall electrolytic-looking caps, but there is no side shot so I can't tell. The only film caps I can find that might be appropriate are some orange drops (which I've seen used on originals). But they don't match what Martin used.

So what did you guys who already built use for C3 and C4?

Thanks,

Mike
So....anyone want to share what capacitor you used for C3 and C4? Looks like electrolytic...
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Potato Cakes

It was posted somewhere in this thread that those are or can be film capacitors. I am using some axial Vishay film caps vertically mounted with some shrink tuning over the exposed lead. Seems to work great.

Thanks!

Paul

Phrazemaster

Thank you Paul. I sourced some orange drops but I think they would look funny there.

Anyone know what the originals used?

Martin, what did you use for C3 and C4?

Thx everyone,

Mike
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rainton

Thank you Paul. I sourced some orange drops but I think they would look funny there.

Anyone know what the originals used?

Martin, what did you use for C3 and C4?

Thx everyone,

Mike

Mike,
as far as I know the vintage units used either Aerovox AUTOPASS radial film caps or CHICAGO PERM-A-CAP radial film caps.

I sourced both but all wer leaking and I couldn't use them.
In the end I bought Wima radial film caps - and stuffed them into the bakelite enclosure of the CHICAGO PERM-A-CAPs  ;D

Looks authentic and works great.

But I've even seen refurbished units with orange drops - looks funky  8)

Phrazemaster

A-ha!

Very clever of you Martin!

Thanks a lot for the detailed info; I really appreciate it!! I’ll see what I can do....

In other news, I received the switch/pot combos from Blore-Edwards. They are glorious! I will post pix when I get a chance.

These make it easy to add a GR/IN/OUT to the front panel without too much fuss.

Thx,

Mike
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Phrazemaster

As promised, here's a snap of the Ed Blore Switch/Pot combo.

Glorious! And it fits...

Mike
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ilfungo

Hi
Sorry for a stupid question:
I have a spare utc A10
Could be used as input transformer?
Could be better to use the utc o-1?
Thanks!

My build is 99.9% finished.. The unit passes the audio signal, it's noiseless,  and sounds pretty good in 2:1 mode BUT.. I can' get a higher rates of compression and higher level of the input signal as well. It seems like the OB2 tube doesn't work properly.. there's no filaments lit and this obviously affects the compression:  in 4/8/12 modes the unit distorts the signal. I've checked OB's socket and its supply is ok. But no deep compression.. The unit works the same with or without the OB2 tube.

Today I've discovered that without 6BC8 tubes the OB2 has the filaments lit..  :o

Any advice please?
« Last Edit: February 24, 2020, 07:28:16 AM by Greebok »

OB 2 should be Very bright and red....You have no power to the tube.....

OB 2 should be Very bright and red....You have no power to the tube.....

If I pull out the 6BC8 the OB2 shines as a normal tube.. If I insert the 6BC8 back the OB2 looks as a dead tube..
I've tried various OB2's but no result..
I checked many times all the cables and wiring..  I couldn't find a mistake.. it's started to drive me mad already:-X

I have the following observation: after inserting the 6BC8 back the OB2 works for several seconds and then fades away..
« Last Edit: February 24, 2020, 11:32:23 AM by Greebok »

Potato Cakes

If I pull out the 6BC8 the OB2 shines as a normal tube.. If I insert the 6BC8 back the OB2 looks as a dead tube..
I've tried various OB2's but no result..
I checked many times all the cables and wiring..  I couldn't find a mistake.. it started to drive me mad  :-X

You have to look at the schematic to see how OB2 and the 6BC8 are interacting. Voltage goes from OB2 to the Plate balance potentiometer (R13) to the voltage divider for 6BC8 (R12/14) and then to the plate connections of 6BC8. The filament for V1 (6BC8) is getting power from the transformer heater winding, V6 (OB2) is not, so V1. Your problem is more than likely somewhere between those points, and it's loading the voltage coming off of the OB2 to down to nothing. Might not hurt to measure C1 and make sure it is indeed 0.1uF and connected properly to OB2 and ground. Also make sure that ground connection of OB2 is also good.

Once again, all of of your eyelets need to be soldered to the traces to ensure that there is a good connection. Same thing for eyelets that are used as vias.

Thanks!

Paul

Yes,
The traces on these boards to be honest really suck with silver solder.......The trace metal must be very
low quality chinese metal. Never had a problem with Chinese boards from PCBWAY
They do not take solder well......
Older lead based solder probably would flow better.

Might not hurt to measure C1 and make sure it is indeed 0.1uF and connected properly to OB2 and ground.

Are you sure about the C1? It's 0.47 uF btw.. Maybe do you mean C10 ?

Might not hurt to measure C1 and make sure it is indeed 0.1uF and connected properly to OB2 and ground. Also make sure that ground connection of OB2 is also good.

I've resoldered the OB2's socket and checked it many times.. The C10 (I guess you mean it namely) is Mundorf Supreme silver oil 0.1uf.
« Last Edit: February 24, 2020, 12:19:02 PM by Greebok »

Potato Cakes

Are you sure about the C1? It's 0.47 uF btw.. Maybe do you mean C10 ?

Yes. C10. Sorry.


 

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