Rerurn to Romy the Cat's Site


In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET
Post Subject: More ansvers.....Posted by Romy the Cat on: 6/4/2015
fiogf49gjkf0d
 anthony wrote:
25 turn pot in the filament supply.  For the life of me I can't source a 25 turn pot.  The 10 turn Bourns 3590 is the closest I can find.  Do I need to keep looking for a more sensitive pot or do you think 10 turn is manageable?
   
Sure it is manageable. This is just pure the matter of comfort.
 anthony wrote:
 The fuse.  You show a fuse on this schematic (that traces back to the B+ supply) but omit it on the 6-Channel schematic that I linked to earlier in the thread.  Do you use this fuse or have you removed it?
  Yes, I use 7.5A slow blow at the very entrance of the 6-Channel schematic with the amp drown in cruse mode in mid of 4A. The slow blow is critical as the amp will start up and begin to saturate the chokes it will draw instantly over 3kW. The normal consumption is 375W if I am not mistaken.
 anthony wrote:
HP Filter 50R.  In the schematic above you use a 50R resistor leading into the 6E6P but omit it on the 6 Channel schematic.  As far as I can tell it is not required for the high-pass RL filter so do you use the 50R or has it been removed?
 
Well, the 6E6P is very fast tube and have tendency for microphonic effect, in particularly while it I cold. It is a common practice to put a very small resistor (50-100R) right before the grid entrance to stop any stray noised to come to the grid and arouse the tube. This is call grid stopper. The ferrite bids serve the same purpose. So, the grid stoppers with fast tube are not part of semantics but rather a part of regular design hygiene and they are implied with those type of tubes. On the 6 Channel schematic I just did not have space to depict it but I still would use it in particularly if your wires from the coil are too long as they act as antenna picking up all imaginable dirt in the amp chasses.
 anthony wrote:
Changing valves.  Could you please explain to me the process of changing valves, say from 45 to YO186?  Please treat me as an imbecile in this regard.  I am very interested in the process and think that it will help me better understand its use.  If I were to guess I would say shut down the amps; remove 45; install YO186; turn on amps; adjust 100R pot to read ???? through the measuring points; press play.  Or maybe it is simpler than that...in some photographs I notice a switch on the "DHT Island" but do not know what it is for.
 
Yes, that is exactly how you describe the process. You adjust the 100R in order to kill the noise on the output. What I do is use mili-voltmeter on the terminal of S2 and try to set the voltage in there under 3mV. I think anything above 20mV is auditable, Anything under 10mV is dead silent. Another very important factor when you change the tube and try to compare them is that they all will have slightly different gain. So here is what I do. My tuner has 1kHz calibration tone, it is convenient and I do not need to bring a generator or test CD). 

1)    Drive the calibration tone and measure the AV at the speaker (I prefer to do it electrically  not acoustically)
2)    Follow your procedures to replace the tubes
3)    Drive the calibration tone with the new tube and measure the SAME AV at the speaker. If the AV not same then use the post OTP attenuator to make it the same. 

There is some “kind” into it. Some tubes you do not mind to drive louder (mostly dark tubes:  PX25, RE604, YO186, 2A3 with single plate for instance) and some you would like to run softer (type 45, 30, 2A3 etc…). You will end up with whatever you prefer eventually. Be advised that the output of Fundamentals, HF and Insertion channels will greatly impact how you would like to hear your MF.

Rerurn to Romy the Cat's Site