Meanwhile I did but the reg won't adjust for whatever reason.
An externally hosted image should be here but it was not working when we last tested it.
Numbers are as expected (anode 140V, Ia 25mA, bias 8.8V) and filament voltage drops nicely from 2.0V to 1.8V when HT is engaged. However, on the inset of HT there's a loud high pitched squeak, unbearable
This feedback sound stopped when the tube was at its side, the grid facing up. I saw you guys busy with teflon tape and shrink wrap so there's hope. Next is a 20KG frame with suspension. Fully agreed, it's a stayer. Cheers Ale! 
Hi Disco,
It looks like you dont have enough voltage drop on the regulator. From my experience,You need at least 5-5.5v volts drop on the regulator in order to be able to adjust filament voltage. If you need 10.6V output, your input should be around 15.6V.
Best,
Radu
It looks like you dont have enough voltage drop on the regulator. From my experience,You need at least 5-5.5v volts drop on the regulator in order to be able to adjust filament voltage. If you need 10.6V output, your input should be around 15.6V.
Best,
Radu
Hi Radu, you're right. The reg lacked the necessary voltage to maintain regulation and dropped out, leaving its output depending on the input voltage. Fiddling with the small screw took too long (risking to burning out the filament) so I'll make a coarse adjustment first with a fixed resistor. The current to ground is 8.8/15=587mA, including the 25mA HT. So the hot filament is representing a resistance of 0.562/1.8=0.31 ohm.
hi Jaap, yes, the regulator needs an overhead of 4,5V minimum. A dropper-resistor in the supply should be set to give about 16V when loaded, for a typical 4P1L line setup, as Radu noted.
The 4P1L filament in parallel mode [2,1V 650mA] should be about equivalent to a 0,33ohm resistor, so you can use a 5W cheap ceramic R as a test/dummy load, and set it up before threatening the filament!
The 4P1L filament in parallel mode [2,1V 650mA] should be about equivalent to a 0,33ohm resistor, so you can use a 5W cheap ceramic R as a test/dummy load, and set it up before threatening the filament!
Rod, no doubt about it the DHT Heater is a fine product. One should be carefull though not to burn out the heater when first installing.
Your recommendation is to use one power supply per DHT Heater? Is that because half the current leaves less residual noise to filter out? In terms of channel separation there's no real benefit, is there? I'm asking because of space restrictions.
Your recommendation is to use one power supply per DHT Heater? Is that because half the current leaves less residual noise to filter out? In terms of channel separation there's no real benefit, is there? I'm asking because of space restrictions.
Jaap, thank you!
I recommend a separate dc supply to feed each regulator, mainly because there is dc-coupling between the supply voltage and the filament. If you have 2 filaments dc-coupled together, this will cause a dc-current to flow between the 2 filaments, if they are at a different voltage.
The most obvious example: when both channels use cathode-bias, and the 2 cathode voltages are different - there will be leakage between one side and the other. This can cause biassing errors, and excess noise.
When both sides use fixed bias (positive output of Regulator is grounded), there is less of a problem, but some minor crosstalk is possible.
I recommend a separate dc supply to feed each regulator, mainly because there is dc-coupling between the supply voltage and the filament. If you have 2 filaments dc-coupled together, this will cause a dc-current to flow between the 2 filaments, if they are at a different voltage.
The most obvious example: when both channels use cathode-bias, and the 2 cathode voltages are different - there will be leakage between one side and the other. This can cause biassing errors, and excess noise.
When both sides use fixed bias (positive output of Regulator is grounded), there is less of a problem, but some minor crosstalk is possible.
I personally don't think a 4P1L as 2 stage driver has near enough gain unless you have obscene speakers, just run the numbers. Thanks Mogliaa, for the post.
Well, if you use 4P1L outputs it does work. 10x10 = 100. Use a 300b and you have 30x3.5 = 100. Drivers like 6N1P and ECC88.
Same would be true of 211 outputs.
But I do see your point with the usual output tubes.
Tried and rejected in my case. The sound with a resistor isn't unpleasant, it's just rather dull and lifeless compared with transformers like LL1660 or plate chokes. I don't use active loads, I haven't yet managed to eliminate traces of hardness and glare, though I haven't tried more elaborate configurations. Active loads are very lively and have good bass.
Pushing around iron I came to these setups. The power resistors dissipate almost 9W (for both channels) so they'll have to go outboard. In the first setup they're out of sight and give a better heat distribution. In the second setup they're closer to the tubes so wires will be shorter and there will be less stray pick up in the cathode from the power supply. I haven't descided yet but I lean toward the second
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Member
Joined 2006
A quick question.
Are the vintage nos 4p1ls (from 70-80s) sonically better than the newer ones currently available on ebay? Thanks!
Are the vintage nos 4p1ls (from 70-80s) sonically better than the newer ones currently available on ebay? Thanks!
Member
Joined 2006
A 4p1l seller asked if I would be interested in getting the vintage 70-80s ones as oppossed to the ones on ebay (from the 90's?) but offering no details on sonic comparison thus I am asking here.🙂
