Hmm. The E1148 tube were a for a tank to tank radio communication in Brittish tanks. Not made for audiophiles in mind at all. Sure this will sound as good as a 6SN7?
I own and listen to a Sun SV-2A3. Stock it did indeed have a kind of polite, not so involving sound. In my case I changed the driver tube to a 6BX7 and changed the OP of the input 6SN7 to 120V@4.5mA/side among other changes. This does require reworking of the circuit and adding a separate filament transformer for the 6BX7. The lower plate impedance of the 6BX7 allows for reduction of the grid leak resistors on the 2A3 grids from 220K to 75K and will result in a "meatier" sound. I also added CCS plate loads to the input and driver tubes, stepped vol. and bal. attenuators, Lundahl input transfomers etc.
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Nice rebuild! I am tempted to try at least a few of those mods. Since my amp is a clone made in China I should upgrade the output transformers. Why haven't you?
Which Lundahl transformer did you use as input transformer and what did this do?
CCS plate load looks interesting but above my level.
I took a look inside the amp and several values are different from the original Sun Audio amp, so I better rebuild it and install a new preamp board, but with a mod to reduce gain on the 6SN7.
Schematics or it never happened. 😉
Which Lundahl transformer did you use as input transformer and what did this do?
CCS plate load looks interesting but above my level.
I took a look inside the amp and several values are different from the original Sun Audio amp, so I better rebuild it and install a new preamp board, but with a mod to reduce gain on the 6SN7.
Schematics or it never happened. 😉
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Sun output transformers are pretty high quality in my limited experience, would not be high on my list of things to upgrade. Sun is Japanese as an FYI.
LL1690. My system is fully balanced, transformer coupled. Both the differential mono-blocks and the Sun are connected to my line stage. Without the input trannies the Sun being connected would unbalance the connections. The line stage has floating line out OTs. That's why I added them.
Actually CCS plate loads are easy to implement.
I have been reading some more. A 6SN7 is apparently two 6J5, and using two 6j5 would probably give the same gain and sound. What would reduce gain is to use two 6P5, a tube that is also very highly regarded. Problem would be to find four matched pairs.
I also found reviews on the previously mentioned E1148 tube. I had my doubt as this was used in radios for Brittish tanks, but it has good user reviews.
Another tube is the 2C22-7193. Some thinks it is fantastic and much better than 6J5, and others say 6P5 is better and will never go back to 2C22/7193.
What I really would like to try is to use only one 6P5 tube per 6SN7 socket to get even lower gain. But that would probably require me to redesign the preamp circuit, and I am not a tube amp designer. Someone wrote that the 6J5 and 6P5 is not a drop in replacement for the 6SN7 socket,because the 6SN7 is dual and the 6P5 is single. The 6J5 and 6P5 use the same pins, but not all the pins as a 6SN7.
The cheapest but not the easiest solution would be to make a new preamp circuit with the low gain mod.
I also found reviews on the previously mentioned E1148 tube. I had my doubt as this was used in radios for Brittish tanks, but it has good user reviews.
Another tube is the 2C22-7193. Some thinks it is fantastic and much better than 6J5, and others say 6P5 is better and will never go back to 2C22/7193.
What I really would like to try is to use only one 6P5 tube per 6SN7 socket to get even lower gain. But that would probably require me to redesign the preamp circuit, and I am not a tube amp designer. Someone wrote that the 6J5 and 6P5 is not a drop in replacement for the 6SN7 socket,because the 6SN7 is dual and the 6P5 is single. The 6J5 and 6P5 use the same pins, but not all the pins as a 6SN7.
The cheapest but not the easiest solution would be to make a new preamp circuit with the low gain mod.
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HI Kevin, his amp is a mock up made in china, probably a power transformer as output : haha.
I dont like set with big triodes very much, too finicky amps to match speakers
You could feed the input into the second triode instead of the first (or put the two triodes in parallel if you don't want one to go to waste), so you only have one stage of gain instead of two...
Yes, but that would change most of the values of the resistors and caps in the preamp, no? I need to learn to simulate tube amp circuits to be sure what I am doing.
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The OPTs are second on my list to change, and good ones are pricey. I need to get comfortable working with tube amps and modding this made in China mock up is a great start. I hope the power transformers are not that bad because good ones are not that expensive. The American $50 transformer I used for a Firstwatt F5 works great.
Not really. If you just go straight into the second triode then no changes are necessary. If you parallel them then you might change the bias resistor, but that's it.
Here are my suggestions:
1. remove the cathode by-pass cap on the input triode (as previously mentioned). This cap is bypassing a 470 Ohm resistor that goes to ground off the 6SN7. Simply remove the cap and keep the resistor in its place.
2. If your output transformer has 3.5K primary (as in the original SUN schematic), then change the 2a3 anode connection to that instead of the 2.5k Primary. This will make your load line flatter, resulting in less distortion with lower output.
Note: An even easier quick-fix might be this: If you are using the 8 ohm connection for your speakers, try the 16 Ohm connection instead and see how it sounds. I am probably assuming too much if you have a china copy... but its still worth trying out. If your horns are 16 ohm them this won't be possible.. but see if your output transformers have 3.5k Primaries... I myself prefer 3.5k load for 2a3.
3. If you are feeling like some kind of slightly more involved mod to reduce the B+ then swap out the 47uF input cap (the 1st one directly after the rectifier) for a 33uF one. Make sure it is fully rated to 500V. While you are at it, you could by-pass these electrolytic power capacitors with any reasonable 500V polypropylene film cap (1uF would be nice, but don't spend the world here - I like the $1 variety for this kind of thing).
To be frank and honest.... your best move might be to go for a different, lower powered amplifier altogether.
Ian
1. remove the cathode by-pass cap on the input triode (as previously mentioned). This cap is bypassing a 470 Ohm resistor that goes to ground off the 6SN7. Simply remove the cap and keep the resistor in its place.
2. If your output transformer has 3.5K primary (as in the original SUN schematic), then change the 2a3 anode connection to that instead of the 2.5k Primary. This will make your load line flatter, resulting in less distortion with lower output.
Note: An even easier quick-fix might be this: If you are using the 8 ohm connection for your speakers, try the 16 Ohm connection instead and see how it sounds. I am probably assuming too much if you have a china copy... but its still worth trying out. If your horns are 16 ohm them this won't be possible.. but see if your output transformers have 3.5k Primaries... I myself prefer 3.5k load for 2a3.
3. If you are feeling like some kind of slightly more involved mod to reduce the B+ then swap out the 47uF input cap (the 1st one directly after the rectifier) for a 33uF one. Make sure it is fully rated to 500V. While you are at it, you could by-pass these electrolytic power capacitors with any reasonable 500V polypropylene film cap (1uF would be nice, but don't spend the world here - I like the $1 variety for this kind of thing).
To be frank and honest.... your best move might be to go for a different, lower powered amplifier altogether.
Ian
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Here is another idea.. What is your source? Digital? if it is, then this mod might be a very nice one. You will need a soldering iron, but its not difficult:
4. The input volume potentiometer should be 100K ohm. You could reduce this by simply by-passing it with a 100k Ohm resistor (input to ground for each channel). You would need two matched 100k 1/4 watt film resistors. Go cheap 1/4 watt film here - the actual value is not so important so long as they are fairly well matched. Hope you have some kind of DMM..
You could consider even lower input impedance (i.e. try 50k.. 20k.. if this gets you in a nice volume range and you like the sound... 😉
Ian
4. The input volume potentiometer should be 100K ohm. You could reduce this by simply by-passing it with a 100k Ohm resistor (input to ground for each channel). You would need two matched 100k 1/4 watt film resistors. Go cheap 1/4 watt film here - the actual value is not so important so long as they are fairly well matched. Hope you have some kind of DMM..
You could consider even lower input impedance (i.e. try 50k.. 20k.. if this gets you in a nice volume range and you like the sound... 😉
Ian
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@Rewind if you want the 6P5's send me a pm. I have a matched quartet of identical Tungsol's new in original boxes and some identical strong testing (90% emission) used Raytheon's which I selected over the years one by one. I stopped collecting these because I decided to use other tubes.
Regarding the mod on your amp I would do as suggested at the beginning. Remove the cathode cap from the first stage. It's the most sensible thing to do.
If this is not enough then you might also evaluate a step-down high impedance input transformer. I know one that has reasonable price and excellent build (mu-metal core) and performance.
Regarding the mod on your amp I would do as suggested at the beginning. Remove the cathode cap from the first stage. It's the most sensible thing to do.
If this is not enough then you might also evaluate a step-down high impedance input transformer. I know one that has reasonable price and excellent build (mu-metal core) and performance.
Thank for your suggestions. I found this old post: http://www.diyaudio.com/forums/tubes-valves/165848-driver-bypass-cap-value.html
It seems you are all right in some way. It confirms that a 20uf cap could be used as suggested in the planned mod. It also seems removing the 100uf cathode bypass cap that bypasses the 470 Ohm resistor sounds fine and would be without hum.
I don't think I have a 16 ohm option on the made in China OPTs, even if my horn channel speakers are 8 ohm.
Yes what I really would like to do is to use a 45 tube amp with a low gain preamp. I wonder how it would sound with my DIY Firstwatt B1 instead. Not sure I am a fan of tube preamps anyway. But I am into the fat juicy magical sounding power tubes, wether it is 45 tube or 2A3. Could I use the B1 directly to the 2A3? I don't think they work the same at all, but it is worth asking.
I also found a popular preamp called Franks preamp that is very similar. Not sure how Frank's preamp would work with the 2A3/45 tubes either. Maybe Frank's preamp is more sophisticated.
http://www.diyaudio.com/forums/tubes-valves/141263-frank-s-6sn7-preamp-linestage.html
MerlinB: I would like to try using only half the 6SN7, but I am not sure exactøy what to exclude of the circuit.
So many options, I am getting dizzy.
It seems you are all right in some way. It confirms that a 20uf cap could be used as suggested in the planned mod. It also seems removing the 100uf cathode bypass cap that bypasses the 470 Ohm resistor sounds fine and would be without hum.
I don't think I have a 16 ohm option on the made in China OPTs, even if my horn channel speakers are 8 ohm.
Yes what I really would like to do is to use a 45 tube amp with a low gain preamp. I wonder how it would sound with my DIY Firstwatt B1 instead. Not sure I am a fan of tube preamps anyway. But I am into the fat juicy magical sounding power tubes, wether it is 45 tube or 2A3. Could I use the B1 directly to the 2A3? I don't think they work the same at all, but it is worth asking.
I also found a popular preamp called Franks preamp that is very similar. Not sure how Frank's preamp would work with the 2A3/45 tubes either. Maybe Frank's preamp is more sophisticated.
http://www.diyaudio.com/forums/tubes-valves/141263-frank-s-6sn7-preamp-linestage.html
MerlinB: I would like to try using only half the 6SN7, but I am not sure exactøy what to exclude of the circuit.
So many options, I am getting dizzy.
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Is this sch supposed to be modified for guitar or hi-fi amp? Sorry have to ask again as your target is very blur to me, but my comment will just stop here you can continue.
No, hifi, but the same idea can be used for guitar as well. I am not happy with the thin sound of the 6SN7 tube preamp I have in my 6SN7/2A3 tube amp, where the thin sounding 6SN7 tubes dominates at low levels. I am after the fat lively sound of the 2A3 or 45 power tubes, which I can hear when cranking up the volume. Guitar speakers are almost as sensitive as my horn speakers and the same sound would be benificial for a training amp used in a home studio.
MerlinB has a good solution... by the way the 6sn7 isn't 'thin' sounding... quite the opposite, it is a very meaty sounding tube with drive and bass, lean on distortion maybe...
this post points again in the direction ----- you want more distortion... lower the voltage of your amp!
Again, Not distortion. I want the chracteristics of the 2A3 tube which I think I like better than 6SN7. You may be right, I have never heard them with less than medium gain. But I believe I have heard when the power tubes take over. Lower the voltage? How?
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