Rerurn to Romy the Cat's Site


In the Forum: Melquiades Amplifier
In the Thread: Bias help
Post Subject: AnswersPosted by Romy the Cat on: 6/5/2013
fiogf49gjkf0d
 DA wrote:
1.How and where to make ground connection to the chassis (signal and power supply and between them)

2.What are the test jacks near the 6c33c for (bais..)? In the photos there seems to be a resistor connected to one test jackand ground to the other but it is hard to see clearly.

3.How to deal with the difference in gain of 6c33c.or maybe it is not an issue.

 
Daniel, here what I did. Do not consider it as something that need to be imitated but that was decision and I have my reasoning behind them. I do not insist that I am right however.

1)  The ground connector to chassis on PS side is at rectifier point. I have all rectifiers sitting pretty much of the same very thick copper wire and that wife is grounded right there. The ground connector to chassis on amp side is right at the entry of RCA jack.  The cables that run between the chassis I think have 4-5 wires for ground but I do not remember if both cables have ground. The DC cable certainly does but I am not sure that filament cables do. I think filament cable has ground only from one side but I do not remember now. I think if they are identical length then you can ground both sides and then, after you test for loops you will be able to lift one if you find it necessary.

2)  Sorry, I do not know what you are asking. What test jacks near the 6c33c? There is nothing on schematics.

3)  The difference in gain of 6c33c is serially might be a problem and I did told about it many times. The gain might be not only as they new but they might age with different speed and gain of the identical tubes might (or might not) slightly drift and the go older. Generally it is not so bad but you will be able to see two new tubes with 1-2 dB gain difference. Some you will see some freak tubes with 3-4 dB of gain different but that is rare. It is very easy to much the tubes by gain. You might use the amp itself to do so as this is a very good tube tester. Burn in the tube that you want to use and then set then to run in the amp. Drive the identical signals to the both amps (I use a generator in my tuner – very convenient) and measure the outputs – as simple as this. You can use the acoustic dB miter but this is not accurate, particularly if you use horns. So, measus the voltage on the speaker line. I have a few Dorrough Loudness Meters w/Percent Modulation and they are after calibration is very accurate and very convent. I use it all time to run them across the channels of my 6Ch amp.
 

Rerurn to Romy the Cat's Site