• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6HJ5 SET

lovely amp there Bird.
I like 45 too but seems like they are pretty expensive now. I therefore wish to try the 6HJ5 for I have couple pair Mullard. I'd go for the Edcor as of your advice. I don't have 6n7 in hand. Could I use 5670 instead? The mu/35 is almost the same as 6n7, but I'm no expert on tube. Don't know if 5670 is suitable, do I have to change the bias point.
Regards
Albert
 
lovely amp there Bird.

Yes and thanks to George for designing such a pretty sounding amp.

I like 45 too but seems like they are pretty expensive now. I therefore wish to try the 6HJ5 for I have couple pair Mullard. I'd go for the Edcor as of your advice. I don't have 6n7 in hand. Could I use 5670 instead? The mu/35 is almost the same as 6n7, but I'm no expert on tube. Don't know if 5670 is suitable, do I have to change the bias point.

Besides pinout the 5670 should work just fine, you don't even need to change operating point and you only need one triode since the rp is about half that of both 6N7 triodes in parallel. That means one driver tube for both channels. In fact simulation shows that the THD is a C___ hair lower than with 6N7's. I chose the 6N7's because I like the looks of the 6N7 metal cans and the 6N7G. I need to post some pics with the 6N7G.
 
6N7G's:hohoho:
 

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Bird,
I almost have all parts in hand, the same ptx with your build, the wood chassis and all other parts but not the opts. I didn't order the opts for the reason that I have a pair Hammond 1640se which can handle 200mA, 1.25k primary with 4,8 and 16 ohm secondary.
I have a new idea to make two mono block with 2 6hj5 in parallel. Therefore I don't have to buy opts, but not sure if the driver is up to the task.
Albert
 
So many options... Those 6AV5 /6BQ6GA are fairly close to 1/2 of a 6HJ5, or to a full 6JN6/6GE5.

12BQ6GA (and 6AV5) in Crazy Drive / Twin Drive: (3.5V steps on g2, 50V/div Horiz., 20 mA/div Vert. I think)

Hi Don

I have some of these and am setting up my driver rig to do crazy drive on them... Are these curves starting at 45V going down? I kind of got this idea from the image name....

Also, did you use Rg2g1 = 2.45K, Rg1k = 2.45K like in your previous post on 12BQ6GTB ?

Best regards
Ian
 
Are these curves starting at 45V going down?
Likely, yes. My early curve tracer setup had limited grid stepping range for g2 drive, so I used a series power supply and subtracted V downward with the stepping. The latest curve tracer version allows me to sweep 0 to +168V, so those are usually traced upward from 0V.

Also, did you use Rg2g1 = 2.45K, Rg1k = 2.45K like in your previous post on 12BQ6GTB ?
Not sure what tube you are referring to. 6HJ5? I think there were some Crazy Drive curves done for that back somewhere. The Rg2g1 resistor may need to be higher in value if you are driving the tube to higher current than I curve traced. I can run another trace to check if you let me know what tube/conditions (max current) to use.
 
My late come 6hj5-5670

Bird,
Here comes my little amp and I still need some more time to finish it for enjoyment. As of the picture, you can find there are 2 5670s, one for each channel. I want to run the 5670 in parallel and see if it sounds better this way. This looks better to me too.
As of data sheet, I have to keep 150v @8.2mA per triode in class A. What if I run both triodes in parallel, Do I have to up the current to 16mA?
Regards
Albert
 

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If you have 240 ohm on each cathode you should be able to just tie them together effectively giving you 120. Do the same with the anodes and just tie them together, the anode load resistance will effectively halve as well. That's the easiest thing to do if things are already wired up. But if you want less clutter I would remove all values for cathodes and anodes and just tie the pins together and use the correct values which would be in half. Are you using a CCS on the anode? If so you will have to change the current set resistor in order to double your current, changing the cathode resistance will only adjust anode voltage. For the 10M45S you will want ~200R.


I await your impressions. When I was trying out drivers for the 6HJ5 I can't remember if I tried the 5670.........I don't think I did. The front end stage does make a difference in overall sonics.
 
I have my amp fired up and everything is in the range. It runs at 300v with the cathode 48.8v and right on the target. The parallel 5670 with a 8.2k anode load and with an adjustable trimmer at cathode to run at around 17mA.
Sound is deep and very quiet background. Lots of low end but the high is a bit on the weak side. It might be the result of the OPT. I'll let it sing a bit longer to give my full impression.
 

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Yeah nah I don't have high ends lol.



Who makes your output transformers? Have you taken any bandwidth measurements to see at what stage your losing the treble? I am curious, I may throw mine back on the bench and see what I get for bandwidth, I forget the results from when I built it but I don't think mine extended up very high.