diytube.com

by **Gregt01** » Mon Mar 05, 2007 5:12 am

Hi Tom and thanks
I did as you said I'm getting 1vdc but not stable,

What next?

What time is it there Tom?

Greg

by **Shannon Parks** » Mon Mar 05, 2007 6:39 am

Greg,

Do you have each of the power tubes with their own 10 ohm resistor to ground or are you sharing a 10 ohm resistor (like in the Mark III circuit)?

by **Gregt01** » Mon Mar 05, 2007 7:11 am

They have there own
Rechecked all resistors ok
10 Ohm .5W

by **Gregt01** » Mon Mar 05, 2007 7:15 am

Good morning Shannon
I still havn't made the changes as per Hammond
Would this cause this?

Greg

by **TomMcNally** » Mon Mar 05, 2007 10:48 am

Hi Greg -

The mods for Hammond transformers are for feedback tweaking, not bias. Are you measuring the bias with the input shorted and a load (speakers or resistors) on the amp ? You can't set it with music playing. If you can't get the bias in range, you may need to adjust the values of the two resistors in the bias supply .... 4.7K and 18K ... you would probably want to try a 10K in the 4.7K spot and maybe go higher, say 22K in the 18K spot. Are you getting about 1 volt on each tube ? The trimpot on the drive board is to balance them, after you get them in the ballpark with the chassis mounted pot. It may take a little back and forth to get it all right.

... tom

by **Gregt01** » Mon Mar 05, 2007 5:11 pm

Tom the resister values were spot on
700 mV for KT88 with room to adjust thanks for that.
No no music threw, short was there and 8 Ohm
load.
Thanks again.

Greg

by **TomMcNally** » Mon Mar 05, 2007 5:24 pm

Let us know when you get the other side playing !

... tom

by **Gregt01** » Mon Mar 05, 2007 7:55 pm

No Problem

Many Regards
Greg

diytube.com

First Power Up

Who is online