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In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET
Post Subject: Keep dong what you do...Posted by Romy the Cat on: 1/3/2019
 anthony wrote:
Looks like I spoke too early.  When I made that statement I'd only tested the voltages in the DHT Channel and they were pretty close to correct...but when I put a tube in there it glowed a little too hot so I quickly shut it down.   Bugger!

What tube do you use? I hope you did not experimented with 4V tubes! When you have the things in test state then get any cheap tubes (45,2a3 etc..) and to experiment on them

 anthony wrote:
Romy, without any DHT tube in place, I have 403V coming out of the big filter cap for the DHT Channel (separate power supply) and 147V/8.3mA at the anode of the 6e5p which is a little higher/lower than the 140V/10mA on your schematic.  I am wondering if this lower current could be the problem?  I added some more resistance to drop the anode voltage and although I thought it was going to drop it 9V it only dropped it 3V, and the anode current remained at 8.3mA.  Tomorrow I will drop the anode voltage further so see if that raises the current.
The DHT channel is direct coupled, so you need to be very careful with it as the plate on the driver tube acts as bias of the DHT. The 147V/8.3mA you got is OK if would not make the DHT to flash. Make sure that when DHT get high voltage the pate voltage of the driver tribe has been stabilized.

 anthony wrote:
It would be great if you could remember some of your time with the DHT Channel.  I've only just got my head partially around your IDHT Channels and this circuit is almost entirely different again. 
Well, the DHT and IDHT are different animals for sure, the driver state look very different for them in my amp and here is the reason. I wanted to use the same driver tube for sure and I want it to be direct coupled. The problem that the 5E6P has too much gain to drive my IDHT directly, so I need to reduce the 5E6P gain. I went to a classic cathode bias. The cathode bias has been wonderful but it has a major problem: the cap on cathode. The cap is need there to get the nominal tube gain but in my care I need to gain. So I left the cathode cap out and get my IDHT the lower voltage it needed. I do not remember the numbers now, you need to look in the thread where I experimented with it. I can post a link if you want me.

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