Drip 175B "modded" first power up problems

[kmozart]

Hi,
I built two 175 b, and added a in-GR-Out meter mod, then replaced the out trafo with the Sowter 1285A for the different ratios.

So far units power up, the voltages are in general low, as here:

Out Transf. Hi and Low -  266, where has to be 295 and the center 276, where has to be 310
C11 Cap  I have 340, and has to be 365
C10 Cap I have 106.4 where should be 108
R37 I have 37.7 where should be 45
On the 6BC8 I have 3v on the tube leg and 80V by the resistor, Where should be 1.8 with 90V


Also, I can not see gain reduction at all, at least on the meter, by sending 1k to the input.

Both units as of now are working in the same manner, at least my error is consistent!


Any help would be appreciated! 

 

[kmozart]

OK,
I figured it out! Hum disappeared after I bridged the 20 DB Pad;  ???

P1 with L1 and P2 with L2!  Now units are working!!

Problem I have now is that I don't hear any compression at 2:1, nor the needle moves.  Same on both!

At 4:1 ratio I think I have LOTS of compression, With Really pumping at 8:1 and 12:1!! 

Any Idea where to look?

I see on the original schematic for 177, where Multi-tap trafo is implemented 12AX7 has 80V  at R23 and R24, mine has 175V!!


I red somewhere that it depends of the resistors used.  Could that be the problem?  ...

On R36 and 37, by the 6AL5, where 45V is needed, I have 20.5V !!! 


Any Help Would be Greatly Appreciated!!

 

[kmozart]

Nobody has experience with these??!?  :-[ 
60 views no help,... 

 

[alexc]

Hi - nice looking build.

I've done a previous version of a Drip 175b - so I've reasonably familiar with the deal.
As well as it's mightier stable mate, the venerable RCA ba-25 -ish  builds.

Let me take a look at your description of what you see and I'll try and assist.
Generally, these are pretty straight forward. So I'll have a read and get back to you.

Btw - when these guys work right, they are quite a desirable piece of kit 

Regards

 

[alexc]

So - what's your 'vital statistics'  ?

- PSU traffo ? Is it a Hammond or what ?
- unfiltered B+ voltage achieved ?
- heater AC volts achieved ?

That's a start to determine whether your PSU  section is right.
Your readings seem to be a bit low. So, that's the first thing to look at.

These guys are very light on 'juice' so you shouldn't be experiencing extended loads on your HV which can cause 'droop' in the B+ you can get.

So - what psu traffo and hat are you measuring? 15V down on expected is prolly no big deal. 25V or so and something is happening. COuld be low mains voltage ? Could be bad wiring or component. Causing excessive current loading and drooping pieces.

My experience with a Hammond PSU traffo is that it can power a battleship before sagging.

 

[kmozart]

Hi Alexc!!

THANKS for offering to help! 
I was so overwhelmed with work last couple of days, that I could not go back to the project. I'm all ears now!

- PSU Trafo Is Hammond 270FX,
- Voltages on the GZ34-TK
- Pin 2 - 7.1 V
- Pin 8 - 5.2V
- Pin 6 - 270.6V
- Pin 4 - 270.7V

I noticed tha on the 770 schematic I have shows that by the resistors R36 and R37 I will have 45V on the ratio 12:1. When I switch to 12:1 ratio, I have  1.26V !  Is there something wired opposite?

Confused!

Really appreciate any help!!

Thanks!!

 

[kmozart]

Just figured out one BIG MistaKe;  I had reversed the order of the resistors on the ratio switch!!! 

Now acts more normal!

 

[kmozart]

Still;  by the point of 80V I'm getting 179V By V2 12AX7

 

[Space Charge Limitef]

Still;  by the point of 80V I'm getting 179V By V2 12AX7

Have you sittef problems out yet?

If not suggest you do the following:

Check voltage out of the mains transformer before rectification. This should as specfided for your transformer.

Check voltage after choke junction of R34 and R35.

If these are as they should be, then you need to check that the DC resistance of your choke is as stayed +- x%

If your chocke is OK and voltage is correct, then chech the value of R44 (I think) the resistor that drops the voltage if you use a transformer other than the one specified.

Tell me what this value is and voltage after choke at junction of previous mentioned resistors and I will calculate it for

Still;  by the point of 80V I'm getting 179V By V2 12AX7

you

 

[kmozart]

I have V2 Build.

For the Main Trafo I have Hammond 270FX. 
Between R43 and R44, (I think you meant that instead of R34 and R35) At the measuring point where it says I have to have 310V I have 270V.

R44 is as stated; 1.5K

I see that the allied electronics 6k56vg has 550V while HAMMOND 270FX has only 508V. Could that be a problem? Is the allied then better suit for this build?  I spent this much I can spend $100 more for the Allied one...

Other problem I have is that after I stuffed the board , I can't see what part is where!  There is no full layout picture of the board I can find on the net!  Having hard time following the parts.

I should've take one high resolution before I stuffed the board! 

 

[Space Charge Limitef]

You need to test the AC voltage from the transformer 270FX. This should be about 550 according to Hammond or more.

Then test DC voltage at input to choke. Not sure what this voltage should be,but it will be around 330. Because the choke will drop voltage depending in your DC resitance and current draw for unit plus V drop of R44.

Either your choke is faulty (  way too high DC resistance, you can measure this) the transfirmer is not developingvthe correct HT. You can measure this assuggested and tgen eliminate either tge transfirmer or the choke. The GZ34 could be dropping too much voltage as well.

Tell me what the voltages are as asked above and I will tell you what's wrong with it.

Would not buy another transformer yet, until you know what the problem is.

Do measurements and get back to me.

 

[Space Charge Limitef]

I have V2 Build.

For the Main Trafo I have Hammond 270FX. 
Between R43 and R44, (I think you meant that instead of R34 and R35) At the measuring point where it says I have to have 310V I have 270V.

R44 is as stated; 1.5K

I see that the allied electronics 6k56vg has 550V while HAMMOND 270FX has only 508V. Could that be a problem? Is the allied then better suit for this build?  I spent this much I can spend $100 more for the Allied one...

Other problem I have is that after I stuffed the board , I can't see what part is where!  There is no full layout picture of the board I can find on the net!  Having hard time following the parts.

I should've take one high resolution before I stuffed the board! 

You need to test the AC voltage from the transformer 270FX. This should be about 550 according to Hammond or more.

Then test DC voltage at input to choke. Not sure what this voltage should be,but it will be around 330. Because the choke will drop voltage depending in your DC resitance and current draw for unit plus V drop of R44.

Either your choke is faulty (  way too high DC resistance, you can measure this) the transfirmer is not developingvthe correct HT. You can measure this assuggested and tgen eliminate either tge transfirmer or the choke. The GZ34 could be dropping too much voltage as well.

Tell me what the voltages are as asked above and I will tell you what's wrong with it.

Would not buy another transformer yet, until you know what the problem is.

Do measurements and get back to me.

However if vin is as low as you say it is, then oroblembis with mains transformer as v should be 550 or there's about. Check that you have wired it correctly at the secondary.


Use RED and REd notvRed and yellow and red and yellow. I think transformer iscok, check your secondary wiring first
If GZ34 had vin of 270 wish you are not going to get More than 291.6 V going into choke and even less after R44. Hence indicates either low output on 270FX. If you measure this (again) and indeed it is 270V.

Problem solved.

 

[kmozart]

Thanks for your help!

AC (red wires) on the trafo are giving me 547V

Then measuring ground with the choke connection on the board, DC, gives me  on one leg 342.6V, on  the other is 334.9V.

 

[Space Charge Limitef]

Hi,
I built two 175 b, and added a in-GR-Out meter mod, then replaced the out trafo with the Sowter 1285A for the different ratios.

So far units power up, the voltages are in general low, as here:

Out Transf. Hi and Low -  266, where has to be 295 and the center 276, where has to be 310
C11 Cap  I have 340, and has to be 365
C10 Cap I have 106.4 where should be 108
R37 I have 37.7 where should be 45
On the 6BC8 I have 3v on the tube leg and 80V by the resistor, Where should be 1.8 with 90V


Also, I can not see gain reduction at all, at least on the meter, by sending 1k to the input.

Both units as of now are working in the same manner, at least my error is consistent!


Any help would be appreciated! 

Make sure that you use the two REd wires on transformer secondary and not the two RED and YE LLOW wires

 

[Space Charge Limitef]

Thanks for your help!

AC (red wires) on the trafo are giving me 547V

Then measuring ground with the choke connection on the board, DC, gives me  on one leg 342.6V, on  the other is 334.9V.

Good. Are you OK now? If not get back to me nd I will fix it for you., so that you get 310 at the 1.5K resistor (  we may change this ).

If we do I will tell you what value to use. You are almost there now.

I would be interested in your feed back on the unit and is it value for the money and does it do as stayed on the tin.