GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET

Post Subject: Do not worry....Posted by Romy the Cat on: 6/5/2015

anthony wrote:
Do you still use the fuse shown in the MF channel schematic linked above (not the 6 Channel schematic)?

This find that this fast blow 100mA in B+ supply of output channel is a good idea regardless. In a minor way I will protect your output tube if case your driver go down, which is very unlikely to happen. In a larger picture: in case you are a skilled builder and confident about your skills then you might drop that fuse and juts to experiment with cheap tube initially. In case you are not so experienced builder (like it was in my case) or in case you have 6Ch huge amp with million wire and great opportunity for confusion and accidents (like it was in my case) the present of that fuse would protect you from pricey mistakes and burning the costly DHT. You might have the fuse during the building and then to short it as the amp will be done and the experiments with output tube are over.

anthony wrote:
Well I would have missed that one...so thanks for that. These will be my first amplifier builds so I will probably miss those kinds of things. Can you think of any others that I will probably miss?

Use a light bold as a fuse during the assembly – will save you a LOT worries.

anthony wrote:
Thanks Romy, but I don't know what you mean by AV in the text above. Do you mean dB?

I mean any AV meter you have, would it be DB, VA/AV, volts or whatever you want. I personally use Dorrough, which are very high resolution led loudness/ modulation monitors. They kind of crazy expensive, completely unreasonable, but from time to time you can pick them up at eBay for sub $20. There are many alternative, analog or digital, when you have 14 channels you would like do not run with your Fluke but to have a nice visual representation of your channel does.

anthony wrote:
One more question. The filament supply of the MF Channel has the hum management circuitry on the 4v secondary...do you also use an artificial center tap on the 2.5v secondary? I just thought that it might be one of those "hygiene" things that you left off the schematic. Likewise for the filament supplies of the other channels.

Nope, that is exactly how it is depicted. I have a dedicated transformer from 120V with two full-fill secondaries, one for 4V and one for 2.5V. The switch of tube always would lead for minor adjusting of the 100R resistor. You would not need to do it always as in most cases you will hear the sound of the tube even with some very minor noise. When you find the tube that you would like to spend time then you would balance the 100R resistor to 0mV at the speaker. In some case you will be able to do it but I might not stay there and will run up and down to +-2-3mV: completely not auditable until you stick you head into the horn, turn off your home appliances and stop traffic in 5 miles radius… :-)

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