Welwyn Wxx series is vitreous enamel wirewound types.
These are very good resistors (viable up to 200 C) and the sound -almost "toneless"- also precise.
I use them everywhere, mostly in R.C. regulators (instead of Mills, if cost is object) and PSUs.
A little disadvantage is minor inductivity.
As anode load or heater bias resistor I prefer non inductive resistors, therefore I use in the first case Mills and second case Dale 50W NH types.
Good choice, another option (not for filament bias) for 2W & 5W are Kiwame, cost no object Mundorf M-Resist Supreme 20W non-inductive, it's wound bifilar.
Well, I've ordered a TKD 2CP-2511 100K pot! I'm getting £85 for painting a ceiling, so I feel justified in spending!Thanks. I am using Lundahl LL2745 OP trafos, wired for minimum output impedance (5.6:1). I doubt I will need much gain, as I am used to passives with no gain.
I just looked through Ale's site, and he says 300 ohms wired in Alt R. I will take his word for it!
Also I plan to buy a Parasound Halo A21 power amp, input impedance 33K, sensitivity 1V; I'm assuming that the output impedance of the 26 pre (Lundahl LL2745 wired in Alt R - 5.6:1) will be low enough to drive the A21. Someone please correct me if I'm wrong!
TKD is the one of the best potmeter. I use Noble and Alps Black also, but IMHO TKD is better -for me-.
Output impedance is below 1k (with 3:1 transformer about 1k), so driving capacity is enough.
Thanks. Especially as I have just ordered an A21! It should be here next week, but the 26 pre won't be finished by then, sadly.
Another question; I have earthed the mains trafo chassis, but do the HT chokes need their chassis grounding? They are Hammond 157G "C" frame types, and are mounted on the wood side plates. One is in the PSU case near the rectifier valve, and the other two are in the preamp case at the back.
Another question; I have earthed the mains trafo chassis, but do the HT chokes need their chassis grounding? They are Hammond 157G "C" frame types, and are mounted on the wood side plates. One is in the PSU case near the rectifier valve, and the other two are in the preamp case at the back.
Well, here's a thing. I bought a TKD 2CP-2511 pot, but the postman just put it through the letter box while I was out (I paid for a signed-for delivery!), and I trod on it when I came home! Bent a couple of pins, so I checked it out with a multimeter, to make sure it still worked. 102k on pins 1-3. Fine, but wiper to pin 1 was weird. The reading rose at the beginning of the rotation, then stayed almost constant (in fact it dropped at one point!) until nearly full rotation, then rose again. Which worried me! I googled the TKD and found a video of the same thing. https://www.youtube.com/watch?v=j398xiUt-Ko So is this normal for these pots? Some of the replies to the video suggest it is.
I'm confused; I can return it to HiFi Collective, but if it's OK I would keep it.
Any experience of this?
I'm confused; I can return it to HiFi Collective, but if it's OK I would keep it.
Any experience of this?
Hi all, I'm looking to try out the 26 DHT in a preamp design. Any idea what the max plate dissipation for this tube is? It's not specified on the sheet, but it seems to that it's a big tube with a big plate and should be able to handle some current. Am I crazy for thinking that this tube could handle 10-20mA with a cathode bias of 2V or so? That might work out to a 2-3W dissipation which seems reasonable for a triode of this size.
http://www.r-type.org/pdfs/26-1.pdf
http://www.r-type.org/pdfs/26-1.pdf
This tube is -moderately- low voltage and low current tube, thus output power is negligible.
If you want few Watts try 10Y/801a tubes.
As you can see in the datasheet, the max. static plate voltage is 180V.
At this voltage and -about- 6mA static anode current the plate resistance is 7k3, thus minimum anode load is 15k (rather 20k).
The safe (and average distortion) operating point is about 160-170V, 5.5..6ma, -11.5...12V grid voltage.
The anode current swing is about 9mA...2mA, the anode voltage swing 100..240V, the plate dissipation is about 1W..0.5W (the average is about 0.85W).
At this voltage and -about- 6mA static anode current the plate resistance is 7k3, thus minimum anode load is 15k (rather 20k).
The safe (and average distortion) operating point is about 160-170V, 5.5..6ma, -11.5...12V grid voltage.
The anode current swing is about 9mA...2mA, the anode voltage swing 100..240V, the plate dissipation is about 1W..0.5W (the average is about 0.85W).
Thanks @euro21
If I were to take the rightmost column as the benchmark for maximum conditions (180V, 6mA ~= 1W plate) then I could probably run 8mA through the tube with a -2V bias which looks like it would work out to ~100V on the plate and still be in the safe zone. As always, an in circuit test will be the most truthful. I'll report back in this thread if I blow anything up
If I were to take the rightmost column as the benchmark for maximum conditions (180V, 6mA ~= 1W plate) then I could probably run 8mA through the tube with a -2V bias which looks like it would work out to ~100V on the plate and still be in the safe zone. As always, an in circuit test will be the most truthful. I'll report back in this thread if I blow anything up
After a month of illness I finally powered up my type 26, and it all checked out on the first channel. So I moved the meters over to the other one and wound the variac up. All good until the magic smoke escaped from the first channel's Coleman regulator. I'd moved the ammeter over and forgotten to re-solder the filament lead to pin 1. So the regulator cooked itself, and now I have to wait for another one.
Bugger.
Bugger.
Similar thing happened to me.
Some month ago I measured/developed 10Y/801 preamp. The equipment working well.
After it I change tubes to another graphite plate ones, but only one tube was in the socket. The other side (open heater pins) R.C. regulator smoked, Q6 (BC547C) transistor and R24 (33R) base stopper resistor died.
Electrically no reason to failure, the worst case current in Q6 about 50mA, Uce about 7-7.5V, so dissipation about 0.35W.
I changed smoked parts, and regulator still working, with tube's heater.
Conclusion: DON'T use low filament current version V7 with open filament pins!
Some month ago I measured/developed 10Y/801 preamp. The equipment working well.
After it I change tubes to another graphite plate ones, but only one tube was in the socket. The other side (open heater pins) R.C. regulator smoked, Q6 (BC547C) transistor and R24 (33R) base stopper resistor died.
Electrically no reason to failure, the worst case current in Q6 about 50mA, Uce about 7-7.5V, so dissipation about 0.35W.
I changed smoked parts, and regulator still working, with tube's heater.
Conclusion: DON'T use low filament current version V7 with open filament pins!
In wrong case R24 dissipation is about 100mW.
0.125W resistor is browned, 0.25 or even 0.5W maybe still alive.
In case of open filament, the CCS power transistor (Q5) B-E diode is open, base voltage is about 0.7V over the negative heater supply voltage.
The Q6 collector is on positive heater supply voltage.
If you use R.C regulator to heater bias, the heater supply voltage would be even 20-30V, so at open filament the Q6 overall dissipation would be grater than 1W!
0.125W resistor is browned, 0.25 or even 0.5W maybe still alive.
In case of open filament, the CCS power transistor (Q5) B-E diode is open, base voltage is about 0.7V over the negative heater supply voltage.
The Q6 collector is on positive heater supply voltage.
If you use R.C regulator to heater bias, the heater supply voltage would be even 20-30V, so at open filament the Q6 overall dissipation would be grater than 1W!