ISO a motorboat

[stajo]

2 separate PSU´s for small signal and output......

Make it one PSU instead, that way you can get same performance with less parts and eliminate the loops....

Thats how I had it b4 starting to investigate boating/grounding. You might be right but my bucks are on the feedback as gangsta.

50/100 Hz is totally cancelled at both configs. DEAD silent in 99 dB speakers. Except for boating.

Dude, tell me how to measure phase instead. I think the the Johnny-sidesailor is closer to that.

 

[flatheadmurre]

One scope probe on input one on output !

If the waves are parallel in phase.

If output inverted out of phase.

 

[flatheadmurre]

Time out is over !!

Hand over the good result now .

 

[stajo]

Woopsie. Fell asleep. Did someone upgrade me? Heres some more adult material.

Left channel: http://youtu.be/g5SiMMQS0yQ


Right channel: http://youtu.be/XqeTSMj_ZVw


Feedback removed

 

[flatheadmurre]

Looks in phase and the 0-16 tap generates more voltage ?

Just to check we got the 0 tap right.

Time to check out the grounding and PSU after that.

 

[stajo]

On left channel the one that I have on output generates double voltage. Right channel other way around.

 

[flatheadmurre]

On left channel the one that I have on output generates double voltage. Right channel other way around.

Ok so 8 ohm load on 16 ohm tap ?

Think you´re on to something here .

 

[stajo]

Ok so 8 ohm load on 16 ohm tap ?

Think you´re on to something here .

You must be Sherlock Holmes! Yes I need to sleap on this. And bake a cake or something

Fresh eyes tomorrow

 

[TheGimp]

The simple test is to put an input signal in and measure the output. Then disconnect the feedback resistor from the opt tap and measure the signal again. If the output decreases in amplitude you have positive feedback ( ti gets bigger when feedback is attached).

The solution is to swap the drive from your phase inverter output to the output tube grids.

 

[flatheadmurre]

If the 0 is right so you don´t use 8 ohm tap as 0 that would get you one positive and one negative tap....

 

[stajo]

If the 0 is right so you don´t use 8 ohm tap as 0 that would get you one positive and one negative tap....

Yes, thats possible because I had the wistle when moving FB from 8 ohm to 16 ohm tap. In that case the cable colours are completely mixed up. I will check it after a little tour to work.

Thanks
Staffan

 

[M Gregg]

In that case the cable colours are completely mixed up.

<<<..thats what happens when you assume things...A bit like have you got discharge resistors on the power supply so you don't get fried..

I also think you need to look at the mounting bolts on the power Tx before it burns out..At least try putting some fibre washers under the screw heads.
This isn't to isolate the power Tx from earth you must Earth the Tx but not create a shorted turn..the stand offs are ok..

Cut a slot across (pic) all the holes that you have used to take the TX cables through the chassis and put some grommets or sleeving over the cables.

Hopfully you can get the op phasing right..at least then you will have a starting point..

Watching with interest..

Regards
M. Gregg

 

[flatheadmurre]

I have the hat type nylon washers for the transformer just measure the hole diam.

Nonmagnetic bolts are another good thing when dealing with transformers.

I agree on the feed and return cable nicely twisted through same hole aproach.

I have a wife enforced clearance sale here all prices are non negotiable (free) and absolutely no returns (if you dare try ) so a plasticbag full of the workbench leftovers is for pickup (CC resistors,PIO caps 8x10mF axial caps and a lot of other more modern stuff which i denie all knowledge of .

 

[stajo]

Thanks guys. Atm, if I remember correctly, I have a toothed washer under one of the legs, which also serves as chassie ground connection from PSU star and yellow/green earth. The other ones is just bolts with regular or no washers if I remember correctly.

I wil decide if I keep this way to large Tx or just mount a smaller one. I think I have something.

I was actually att a very well sorted bolt dealer the other day, thinking to buy nylon bolts for this kind of mounting (for a pair of chokes that was). One M4 12 mm had the price of more then I bought the pair of 130 H chokes for

So isolate 3 legs and keep one with toothed washer, is that ok. Plus the wire adjustments?

Best regards
Staffan

 

[flatheadmurre]

You´re not looking for electrical isolation but magnetic here.

You want to avoid magnetic shorts causing losses giving heat.

One ground point is needed for safety so 3 insulated one grounded is fine.

 

[stajo]

A little report on the work then.

I Think I have figured out the taps now.

Ch 1:
Cotton Yellow: Gnd
Plastic Orange: 8 ohm
Cotton Black: 16 ohm

Ch 2:
Plastic Yellow: Gnd
Cotton Yellow: 8 ohm
Cotton Black: 16 ohm

All outputs in phase with input and 16 ohm taps give double sine then 8 ohms.

Then I applied FB again, moved it from Gnd to 16 ohm taps. Outputs now very much lower but still in phase. 1 k resistors in again.

So phasewise I think Im home. Plugging it to the listeningstuff its silent again but alot lower output. I can max volume and its just above relax volume. Hardy 11 watt on my 98-99 dB speakers. And I have a small boating again. Smaller then before but there on both channels.

 

[Zen Mod]

make proper LTP on input , with decent CCS in tail fed from neg PSU , then bring feedback to inside LTP half grid

with that cheapskate approach schematic , you are biting air all the time

 

[flatheadmurre]

Powersupply rebuild .

One powersupply with a nice busbar layout and if it isn´t quite enough put in a 3 leg reg before gainstage.

The powertubes are matched good enough ? just asking....

Do you have the right values in the feedback loop ?

The low output could indicate it´s a 0-4-8 secondary ??

It´s an challenging amp .

 

[stajo]

Powersupply rebuild .

One powersupply with a nice busbar layout and if it isn´t quite enough put in a 3 leg reg before gainstage..

Yea it could have a lookover. I hardly think that has anything to do with the gain though.

The powertubes are matched good enough ? just asking.....

Yea. Good matched.

Do you have the right values in the feedback loop ?.

I have a 1 k, but I will need to measure what the splitter delivers to the output tubes. I think it shall be around 10-12 volts if all is correct with a decent input VRMS.

The low output could indicate it´s a 0-4-8 secondary ??.

Mmm, maybe. Those should be from SCA-35 but you never know. As far as I know only some modern replicas have had 4-8 ohm taps. I measured them, one in Circuit and one over only windings and got 9-11 mH. I dug up a pair of Edcors 8000 to 4 ohms same size with 7,5 H and one pair 8000 to 8 ohms with 14,5 H.

Next step was much bigger, around 60 mH between 8 and 16 ohms, and 140-160 mH 0 to 16 ohms. Which doesnt really makes sense to me but thats about what the LCR tells me. I have nothing in the size to compare with though.

It´s an challenging amp .

Yea. The funnier. I have to go over the circuit again but my back is killing me today.

 

[flatheadmurre]

To find out the turns ratio you really need to apply AC voltage to primary and read what you get on secondary.