Thanks for to all those who chimed in about output transformer impedance etc. Contrary to my perfectionist nature (a curse) I'm going to complete the build with the transformers supplied. Try different tubes and find the ones I like the best.
I do have a question about the 1uf cap in on the presence control. The layout diagram (which I've been told is wrong) shows a 1uf while the schematic demonstrates a 1uf electrolytic. I have three 1uf (@250v)to try and one electrolytic (@450v) any opinions??????
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In many cases a film capacitor can be used anywhere a electrolytic cap can be used.
With the exception of power supplies, and even there I have seen amps use them.
E caps pack more capacity in a smaller package.
But use your ears and decide what you like the best.
I think on ODS #124 there is a Tantalum cap for the presence cap.
Structo wrote:I think on ODS #124 there is a Tantalum cap for the presence cap.
I've seen tantalum and film in Dumble pics. I've tried tantalum, electrolytic and several film caps. Overall I like the film better, and the type of film makes little if any difference. I have a few 1uF Xicon MPP which work well, and I've tried Mallory 150 .68uF as well.
The .68 moves the frequency of the presence knob up for more shimmer than grit. I've also tried 2.2uF film for more mids, but overall the 1uF film seems to fit this amp best. JMO
Indeed a good clean execution.! That use of 1N4007s with big snubber ceramic caps in the HV power supply is pretty old style. Lower cost than hexfreds but takes up more real estate. I assume that was part of the kit?
dreric,
Congratulations, build is looking good. I'd have to say though, if there is any way you can get a PI trimmer in there it will make a ton of difference!
Yes the stock D'lite layout is a bit different from a Dumble and putting the trimmer on the PI forces you to alter the board with new eyelets.
Or as one member did, you can make a small daughter board with the parts on it and mount it on the board mount bolt on the corner there.
Here is a layout I modded to show the PI trimmer.
It does help to achieve better overtones and bloom to have the trimmer there.
I have 110K/ 120K plate resistors on my PI and a 10K trimmer.
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Thanks for the kind replies. I will fire it up this weekend. To answer questions.
Variac = yes
PI trim = yes when I have a chance, I want to see that everything else works.
Scratch build = yes chassis and boards from RJ
1n4007 with snubbers = what I had and I think they look cool (sometimes i can't help it)
Tubes to start = 6V6 the output transformer is more matched to them and KT66s than 6L6s plus I have a ton of 6V6
I am thinking that I will have to increase the value of the bias resistor. The schematic shows the bias voltage at 45V going into a 470 ohm resistor. My transformer is putting out 160V, I'm not sure what value to increase it to. In my feeble understanding of ohm's law I get 100K.
I finally have some time to finish up this project, life's been crazy lately. I've tweaked the bias resistor a bit to get me to usable range for 6V6 or KT-66 tubes which is what I want to use in this build.
When firing it up nothing blows up, which I take as a good sign, but there is no sound. Nada, nothing!
I've gone through about 80 times looking for shorts, reheated / flowed the solder connections nothing. When switching from on to off there is a signal that comes through as the amp is powered down, other than that no sound.
From reviewing other posts it seems the next thing is to measure the voltages on the tubes. I started being over my head a while back so any help is apprecited.
The d-lite schematic doesn't list voltages and I haven't been able to find a voltage chart anywhere. I'm hoping someone in the group will see a pattern and offer suggestions
