Saurav said:
My RCA 5U4G is close to the size of the 2A3. It did give me a problem on by beta 300B as it nearly touches the choke, so I changed it to a 5AR4 (of course adjustments made to compensate for higher voltage due to lower voltage drop of the rectifier).
If I have a chance and applicable to the circuit, I'd go for a 5AR4 due to the slow voltage rise inherent on this tube.
Damper/efficiency diodes
If you really want a slow power-up, why not use TV damper/efficiency diodes? They have stunning insulation between their heaters and the cathodes, which slows down their warm-up time. Most have top-cap cathodes, but the 12CL3 brings all its connections out onto a B9D (Magnoval) base. It needs a 12.6V heater though. Perhaps you could use a little 12V toroid under the chassis?
There was a thread on these diodes on this forum recently...
Ah, you should have specified that it was to be used by other people...
How about a rotary mains switch? That way, you can put the electrical switch at the back (where it belongs) and extend it with a 1/4" shaft to the front.
If you really want a slow power-up, why not use TV damper/efficiency diodes? They have stunning insulation between their heaters and the cathodes, which slows down their warm-up time. Most have top-cap cathodes, but the 12CL3 brings all its connections out onto a B9D (Magnoval) base. It needs a 12.6V heater though. Perhaps you could use a little 12V toroid under the chassis?
There was a thread on these diodes on this forum recently...
Ah, you should have specified that it was to be used by other people...
How about a rotary mains switch? That way, you can put the electrical switch at the back (where it belongs) and extend it with a 1/4" shaft to the front.
Damper diodes - I read those discussions, but decided to stay with more conventional rectifiers for my first attempt. I can always try that as an upgrade. How large are those tubes?
Well, one can always hope
Once I'm off the internet, this is a pretty lonely hobby...
The rotary mains switch is a good idea. I thought of another option, I could put the power switch on the side panel of the chassis, in the back near the PSU circuitry. Since this amp is going to be on the top shelf of my rack, that should be fairly easy to reach. Also, it'll make for an interesting look, because I can put binding posts and RCA connectors all on the side panels.
Has anyone made carrying handles for their amps? All I have is a little 300V 200mA Hammond power transformer, and this is already heavier than anything else I own. I thought about screwing on carrying handles to the side surfaces (when I was thinking of putting switches and connectors on the back), but I'm not sure if that will put too much of a flexing stress on the aluminum with the heavy transformers in the middle of the chassis. Also, with the transformers now off to one side, the weight distribution becomes uneven. Maybe I should just not worry about this. Or put in one handle in the back, close to where the weight will be.
Well, one can always hope
Once I'm off the internet, this is a pretty lonely hobby...The rotary mains switch is a good idea. I thought of another option, I could put the power switch on the side panel of the chassis, in the back near the PSU circuitry. Since this amp is going to be on the top shelf of my rack, that should be fairly easy to reach. Also, it'll make for an interesting look, because I can put binding posts and RCA connectors all on the side panels.
Has anyone made carrying handles for their amps? All I have is a little 300V 200mA Hammond power transformer, and this is already heavier than anything else I own. I thought about screwing on carrying handles to the side surfaces (when I was thinking of putting switches and connectors on the back), but I'm not sure if that will put too much of a flexing stress on the aluminum with the heavy transformers in the middle of the chassis. Also, with the transformers now off to one side, the weight distribution becomes uneven. Maybe I should just not worry about this. Or put in one handle in the back, close to where the weight will be.
12CL3 is remarkably small - smaller than a 6SL7.
Experience with unenlightened/unenthusiastic users shows that that the on/off switch has to be at the front or it will not be used...
Just you wait (weight). Bigger amplifiers require even weight distribution and handles. This is a problem for the future.
Experience with unenlightened/unenthusiastic users shows that that the on/off switch has to be at the front or it will not be used...
Just you wait (weight). Bigger amplifiers require even weight distribution and handles. This is a problem for the future.
FWIW, here are images of the amp from the Angela website:
As you can see, almost identical to your layout, just with all the iron rotated by 90 degrees.
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.
As you can see, almost identical to your layout, just with all the iron rotated by 90 degrees.
Hmmm, there's very little difference.
There's very little difference. Their version allows better cooling, but if you move the 2A3 up the chassis, my layout might be almost as good. In terms of electromagnetic induction, I think my layout may be better. There's really not much in it. Moving the 6SL7 closer together is worthwhile because it allows good point to point wiring.
Go for the efficiency diodes now. They're difficult to retrofit.
You need to convert your other half. What are you going to do when you want to introduce a pair of huge transmission-line loudspeakers into the living-room? You will need to be able to convince her that they are worthwhile, and that starts with education now...
There's very little difference. Their version allows better cooling, but if you move the 2A3 up the chassis, my layout might be almost as good. In terms of electromagnetic induction, I think my layout may be better. There's really not much in it. Moving the 6SL7 closer together is worthwhile because it allows good point to point wiring.
Go for the efficiency diodes now. They're difficult to retrofit.
You need to convert your other half. What are you going to do when you want to introduce a pair of huge transmission-line loudspeakers into the living-room? You will need to be able to convince her that they are worthwhile, and that starts with education now...
That's the one I'm going with. I don't think heat will be that much of an issue, it's hum that I'm more worried about.
I was planning on using both triodes in a single envelope as the upper and lower triodes of the SRPP. So, each 6SL7 serves one channel. Why would having the tubes close together make a difference? I'll be running individual grounds for each channel too, FWIW.
I think I'll try that in a future project then, assuming I build any more amps
I've already bought the 5AR4. Where can I buy a 12CL3? I didn't find any on eBay, nor on Triode Electronics.LOL!! Well, she's living with this right now, so...
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.
I think I'm pretty lucky, in the overall scheme of things
Those are the sealed "bookshelf" versions of the Adire HE12.1s. 96-97dB, 12" woofer with coaxially mounted 1" compression driver.
Saurav said:
I think you might do better to use one valve to cope with the low cathode voltage stuff, and another where the cathode is at a higher voltage. Stereo crosstalk within valves is much exaggerated.
A quick search brought up 12CL3 at very reasonable prices.
Education is a wonderful thing, and if you can persuade your other half to use the existing kit, who knows what you can get away with later? One step at a time.
Making stereo amplifiers with low hum tends to be awkward unless you have a common earth bus bar, hence the comment about moving the 6SL7s closer together.
That would help because I wouldn't have to use a voltage divider to keep the heater midway between the cathode voltages of the two SRPP triodes. However, that would also require yet another transformer under the hood, because the two triodes would now have their cathodes at very different potentials, and I couldn't feed them from the same heater.
OK, I found 12CL3s at thetubestore.com, and they are cheaper than the 5AR4 that I bought. I'll definitely try that out in the future.
She tolerates it, I'm not sure how much she uses it though. One of her friends told her she's very "accomodating" to allow those speakers in the living room.
Fragman56,
I like them a lot. Their strengths are liveliness and dynamics, especially in the midbass. Compared to my last speakers (GR Research Paradox 1s), they aren't quite as refined in the midrange and treble. I've tweaked mine quite a bit from stock, and those tweaks helped quite a bit. My crossover has been modified to raise the upper treble (12KHz+) by a couple of dB, I've removed the dustcap from the woofer and coated it with shellac, liberally used polyfill on the basket legs and around the motors, and my amps have a 75Hz high pass filter on them (cap between the input RCA and tube grid). IMO all of these have helped, some more than others.
Saurav said:
Um. Not quite. Nothing has changed. You've just exposed a slight weakness in the original design. Fortunately, Octal valves can tolerate this treatment, but it would be nicer not to hammer them.
Believe me, education is a good thing. Your other half is perfectly capable of hearing how much nicer your system is - but you're going to have to make it easy to use. This isn't a disadvantage - you get it too!
Hmm... are you saying that I still use the voltage divider to raise the 6V winding up to around 80V, and run that to both tubes? Then the heater will be high for one whole tube and low for one whole tube, instead of being high for one triode and low for the other triode in the same envelope. Did I understand you correctly?
So you're saying that it would be nice if I used a second 6V transformer so that I could keep heater voltage close to cathode voltage on both tubes, but it's not essential? Maybe I should just go ahead and do that... I saw a 6V transformer with sufficient current rating on eBay once for just a few bucks.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.