Hi all,
I've completed stuffing a SimpleSE board with nice results so far. The only thing I'm hung on is what to set the Cathode Bias resistor to. I'm debating if I should set it to a fixed 560 ohm or to be switchable between 750 ohm, 560 ohm, and 430 ohm via 3 position toggle. The settings would be for EL34, 6L6GC, and KT88 respectively.
Question 1.
Is a switchable bias worthwhile or will 560 do?
Question 2.
Am I likely to fry myself having the bias attached to a toggle switch? The specs on the Philmore switch look good, but I may be missing something.
I'll be using the following iron:
Hammond 1628SEA OPT's
Hammond 274BX Power Transformer
Hammond 193H Choke
I've completed stuffing a SimpleSE board with nice results so far. The only thing I'm hung on is what to set the Cathode Bias resistor to. I'm debating if I should set it to a fixed 560 ohm or to be switchable between 750 ohm, 560 ohm, and 430 ohm via 3 position toggle. The settings would be for EL34, 6L6GC, and KT88 respectively.
Question 1.
Is a switchable bias worthwhile or will 560 do?
Question 2.
Am I likely to fry myself having the bias attached to a toggle switch? The specs on the Philmore switch look good, but I may be missing something.
I'll be using the following iron:
Hammond 1628SEA OPT's
Hammond 274BX Power Transformer
Hammond 193H Choke
1. yes, switchable cathode resistors are a good idea if you want to quickly test/listen to different tubes on the fly.
2. The best way of doing this is to always leave one resistor in the cathode circuit; i.e. the 750 ohm one, and then parallel other resistors that when connected across the 750 ohm one will give you the desired value - i.e. 560 ohms, etc. Use a toggle switch and you can switch in/out all three values.
Hope this helps.
-- josé k.
2. The best way of doing this is to always leave one resistor in the cathode circuit; i.e. the 750 ohm one, and then parallel other resistors that when connected across the 750 ohm one will give you the desired value - i.e. 560 ohms, etc. Use a toggle switch and you can switch in/out all three values.
Hope this helps.
-- josé k.
The issue with a switch is that some are break before make, and some are make before break. Consequently, for an instant you will have no cathode resistor, or parallel cathode resistors. Whether this is of any consequence or not, I don't know.
Big wirewpund ceramic pots are still available at hamfests. I got a handful of 25 watt 1K Clarostats or Centralabs for a dollar each at the last hamfest I attended. I think something like that would be a better solution.
After burning out my Bendix transformer, the present iteration of my SimpleSE uses a 330-0-330 transformer, and with this transformer, I use a 470 ohm cathode resistor to set the bias.
I just change rectifier tubes to control the voltage drop and consequent dissipation from big tubes (KT88/6550) to not so big tubes (6L6). I acknowledge this is a cheesy way of doing things, and I'm not advocating it, but for my particular situation, it works. The amp is the PA in our home theater system so it needs to be able to run all day and most of the night while staying very cool to the touch (5Y3 and 6L6), but if I just want to listen to tunes then I can change to something like 5AR4 and 6550 and it will still work reasonably well without going inside the amp.
George's SimpleSE is really a great amp project. I bet that optimized for a specific tube, and with really good transformers, it sounds spectacular. Even with my highly compromised setup, and average (Transcendar) transformers, it sounds awfully good.
Win W5JAG
Big wirewpund ceramic pots are still available at hamfests. I got a handful of 25 watt 1K Clarostats or Centralabs for a dollar each at the last hamfest I attended. I think something like that would be a better solution.
After burning out my Bendix transformer, the present iteration of my SimpleSE uses a 330-0-330 transformer, and with this transformer, I use a 470 ohm cathode resistor to set the bias.
I just change rectifier tubes to control the voltage drop and consequent dissipation from big tubes (KT88/6550) to not so big tubes (6L6). I acknowledge this is a cheesy way of doing things, and I'm not advocating it, but for my particular situation, it works. The amp is the PA in our home theater system so it needs to be able to run all day and most of the night while staying very cool to the touch (5Y3 and 6L6), but if I just want to listen to tunes then I can change to something like 5AR4 and 6550 and it will still work reasonably well without going inside the amp.
George's SimpleSE is really a great amp project. I bet that optimized for a specific tube, and with really good transformers, it sounds spectacular. Even with my highly compromised setup, and average (Transcendar) transformers, it sounds awfully good.
Win W5JAG
I suppose I could also take the rectifier road. I could replace the 5AR4 with a 5U4GB and drop the voltage for the EL34's using a 560 ohm bias. I'm afraid that I won't get full potential from the KT88's with 560.
I'm generally very cautious when making changes to thing. I shut down the amp, make the change, allow it to cool and then fire it up again.
Another question I have is where to place the resistors in relation to the switch. I figure having the resistors before the switch would put the least amount of stress on the switch.
I'm generally very cautious when making changes to thing. I shut down the amp, make the change, allow it to cool and then fire it up again.
Another question I have is where to place the resistors in relation to the switch. I figure having the resistors before the switch would put the least amount of stress on the switch.
whitelabrat said:
Look at the attached circuit to get an idea. Use a double pole 3 throw switch or a separate switch for each channel.
If the fixed cathode resistor is 750 Ohms (switch in the open position) , then use 1.1kOhms and 2.2kOhms to get 430 Ohms and 560 Ohms respectively.
-- josé k.
Attachments
A 560 ohm resistor is a good compromize for all 3 tubes. It runs the EL34 at about 23 watts dissipation which is 80% of maximum. The 6L6GC runs at about 25 watts which is closer to maximum. Use good 6L6GC tubes that can handle it. The KT88 runs about 29 watts which is slightly low.
These measurements were made with 430 volts of B+, and will vary with applied voltage and the individual tube characteristics.
I have a 560 ohm resistor in my amplifier, and parallel it with a 1K ohm resistor for KT88 use. This runs the KT88's at about 40 watts which is no problem for the Electro Harmonix tubes. I use the low tech approach. The board is stuffed with 560 ohm resistors, and I have two 1K ohm resistors with aligator clips on the leads for use with KT88's.
You can put 560 ohm (or higher) resistors in your board, and use a switch to add a parallel resistor as needed. A simple DPST switch can be used. The voltage is about 50 volts max and the current is under 100 mA.
Three different values can be accomodated in the same manner. Put a 750 ohm resistor in the PC board. Use a DPDT center off switch to switch either a 1K ohm or a 2.2K ohm resistor in parallel with the 750 ohm resistor. In the center "OFF" position, you are using the 750 ohm resistor by itself. In one "ON" position you have the 750 ohm resistor in parallel with a 1K resistor giving 428 ohms. In the other "ON" position you have the 750 ohm resistor in parallel with the 2.2 K ohm resistor giving 559 ohms. Again the switch requirements are minimal.
These measurements were made with 430 volts of B+, and will vary with applied voltage and the individual tube characteristics.
I have a 560 ohm resistor in my amplifier, and parallel it with a 1K ohm resistor for KT88 use. This runs the KT88's at about 40 watts which is no problem for the Electro Harmonix tubes. I use the low tech approach. The board is stuffed with 560 ohm resistors, and I have two 1K ohm resistors with aligator clips on the leads for use with KT88's.
You can put 560 ohm (or higher) resistors in your board, and use a switch to add a parallel resistor as needed. A simple DPST switch can be used. The voltage is about 50 volts max and the current is under 100 mA.
Three different values can be accomodated in the same manner. Put a 750 ohm resistor in the PC board. Use a DPDT center off switch to switch either a 1K ohm or a 2.2K ohm resistor in parallel with the 750 ohm resistor. In the center "OFF" position, you are using the 750 ohm resistor by itself. In one "ON" position you have the 750 ohm resistor in parallel with a 1K resistor giving 428 ohms. In the other "ON" position you have the 750 ohm resistor in parallel with the 2.2 K ohm resistor giving 559 ohms. Again the switch requirements are minimal.
Very good ideas! I am enlightened.
I think that the 560ohm resistor with a parallel 1K ohm resistor will do the trick! Sort of a turbo switch for the KT88. I'll probably start out with Shuguang 6L6GC's that I've already got, and later put in the old used Chinese KT88's I've got. I've also got a quad of SED EL34's but those are for another amp.
Thanks all!
I think that the 560ohm resistor with a parallel 1K ohm resistor will do the trick! Sort of a turbo switch for the KT88. I'll probably start out with Shuguang 6L6GC's that I've already got, and later put in the old used Chinese KT88's I've got. I've also got a quad of SED EL34's but those are for another amp.
Thanks all!
The Shuguang 6L6GC's seem to take all the abuse that I can throw at them. No problem with 560 ohm. I have a lot of old Chinese KT88's from about 10 years ago. These will remind you that the Chinese invented fireworks. I have seen some of them red plate at 20 watts, and arc over internally at less than 400 volts. If your old KT88's are this old, be wary of them. Run them with the 560 ohm for a while before hitting the Turbo button.
I use a 1K ohm resistor with the EH tubes because they can take it. I would pick a higher value (say 1.2 or 1.5 K) with other tubes. The EH tubes have additional heat rediating fins welded to the plates.
It is interesting to note that cranking up the tube current provides only a very small increase in power output (less than 1/2 watt). It does however lower the distortion and increase the damping factor. On my big speakers it provides better bass.
I use a 1K ohm resistor with the EH tubes because they can take it. I would pick a higher value (say 1.2 or 1.5 K) with other tubes. The EH tubes have additional heat rediating fins welded to the plates.
It is interesting to note that cranking up the tube current provides only a very small increase in power output (less than 1/2 watt). It does however lower the distortion and increase the damping factor. On my big speakers it provides better bass.
I was looking at the SimpleSE and thought if I built one it would be fun to try different tubes and therefore need to roll cathode Rs.
I was wondering if they made those 2 and 3 pin terminal strips in one pin so you could just screw in different cathode Rs.
I didn't see a one pin in the Digikey catalog. Anyone know if there is a part that would do this?
There is obviously the switch option mentioned above. I suppose that would be worth a try but something about a PCB makes me not want to run lots of extra wires off the board.
I was wondering if they made those 2 and 3 pin terminal strips in one pin so you could just screw in different cathode Rs.
I didn't see a one pin in the Digikey catalog. Anyone know if there is a part that would do this?
There is obviously the switch option mentioned above. I suppose that would be worth a try but something about a PCB makes me not want to run lots of extra wires off the board.
Well I was looking at the pictures. I suppose you could buy four extra two pins and then break one of the pins off and they might fit in the place where the ends of the cathode resisters are. Good or bad idea?
The instructions say something about the R not being to far off the board. Don't know why, particular if you are going to reverse wire it and put the non-tube components on the back.
The instructions say something about the R not being to far off the board. Don't know why, particular if you are going to reverse wire it and put the non-tube components on the back.
I have never seen one with only one pin.
It is a good enough idea that I am going to try it. I currently have a box full of resistors with aligator clips on the leads. I just clip one across the existing cathode resistor when I want to "turn up the boost".
That statement was meant for the builder who puts the resistors on the top of the board and the other parts on the bottom. The requirement is so that the resistors are below the level of the tube sockets and don't touch the chassis. I wrote the instructions asking the builder to place the resistors on the top side of the board to lessen the possibility of putting the wrong parts in the wrong holes, since the board is silkscreened on the top side only. The SimpleSE is a popular project for first time builders, so I tried to make it as simple as possible. It is perfectly acceptable to put the resistors on the bottom of the PC board, but you need to be carefull about placement since the resistors go on first and all of the holes in the board are empty.
After seeing some of the uncharitable comments about the Simple SE on one of the other threads, I thought it was time to do a little experimenting with mine. With the Hammond 374BX I think I was getting around 480V B+ with a GZ34 rectifier. This was fine for my JJ E34L and JJ KT88 valves, but a bit too much for the Wing C EL34 and some Soviet 6P3S (6L6GT) valves I had. One of the Wing C EL34s would glow a dull red, as would the 6P3S. I have 560R cathode resistors, so just replaced them with 820R with switcheable parallel 1.0K and 2.2K, so I have 820R, 597R, and 450R. So far it looks OK. Using a 5U4G to drop a few volts and the selectable resistance looks like it may have stopped the glowing plates. Will have to wait till it is a bit darker to confirm. From brief listening, still like the EL34s and E34Ls. Will put the 6P3S valves back in to see if they settle down a bit. Not quite as detailed as the EL34s.
Still having fun with this amp! Thanks George! Don't let the (one) negative comment/person stop your enthusiasm. We do appreciate the time you spend on the projects and on this forum
Chris
Still having fun with this amp! Thanks George! Don't let the (one) negative comment/person stop your enthusiasm. We do appreciate the time you spend on the projects and on this forum
Chris
Simple SE with 6n3c-E Tubes
This is my first post here. I have recently completed the tubelab Simple SE amp and wanted to give a big thumbs up to George. I have run 4 different tube types (KT-88, El-34, 6550C, and now the Russian 6n3c-E). I have tried 2 different output transformers (Edcor xse15-8-5k and Transcendar 5K SE). So far I have only been brave enough to hook up some cheap minipod speakers (that I tweaked the crossover capacitors on) for listening/testing.
This is a great little board to play with !!! The sound is very similar to my $2000 Cary amp and with these cheap Russian 6l6's I have a little over $200 invested in the current set-up. Tremendous.
I am running the 560 cathode resistor and a Russian k-40 as coupling cap. Also, am using the 6K7VG Allied power tranny, 90 uf of motor run supplemental power supply capacitance and the recommended Triad choke and tube rectification( Sovtek 5AR4). Oh yes, I am using triode mode with NFB after trying all the different combos.
I haven't had this much fun since the fourth grade.
This is my first post here. I have recently completed the tubelab Simple SE amp and wanted to give a big thumbs up to George. I have run 4 different tube types (KT-88, El-34, 6550C, and now the Russian 6n3c-E). I have tried 2 different output transformers (Edcor xse15-8-5k and Transcendar 5K SE). So far I have only been brave enough to hook up some cheap minipod speakers (that I tweaked the crossover capacitors on) for listening/testing.
This is a great little board to play with !!! The sound is very similar to my $2000 Cary amp and with these cheap Russian 6l6's I have a little over $200 invested in the current set-up. Tremendous.
I am running the 560 cathode resistor and a Russian k-40 as coupling cap. Also, am using the 6K7VG Allied power tranny, 90 uf of motor run supplemental power supply capacitance and the recommended Triad choke and tube rectification( Sovtek 5AR4). Oh yes, I am using triode mode with NFB after trying all the different combos.
I haven't had this much fun since the fourth grade.
6n3c-E / 6P3S-E Testing
I just wanted to clarify the Russian tube I am using. This is the -E version of the 6P3S tube that has cyrillic (sp?) lettering of 6n3cE. This is sold on ebay as being a 6L6GC replacement. I tested my wall voltage with my Fluke 179 multimeter at 124.5 volts. This really gave me pause to put in a tube I was "somewhat" unsure of the limits. Testing with the same meter at the points on the Simple SE board that should be the plate and B+ I get 450 and 475 volts , respectively. I had ordered 25 of these tubes and just picked 2 at random, untested and plugged them in.
I am now listening to Yo Yo Ma ( after Pat Metheny earlier) and these tubes appear to be happily making excellent sounding music. These 25 tubes cost me $120 delivered.
thanks to you again, George ; Keep up the good work!!!
I just wanted to clarify the Russian tube I am using. This is the -E version of the 6P3S tube that has cyrillic (sp?) lettering of 6n3cE. This is sold on ebay as being a 6L6GC replacement. I tested my wall voltage with my Fluke 179 multimeter at 124.5 volts. This really gave me pause to put in a tube I was "somewhat" unsure of the limits. Testing with the same meter at the points on the Simple SE board that should be the plate and B+ I get 450 and 475 volts , respectively. I had ordered 25 of these tubes and just picked 2 at random, untested and plugged them in.
I am now listening to Yo Yo Ma ( after Pat Metheny earlier) and these tubes appear to be happily making excellent sounding music. These 25 tubes cost me $120 delivered.
thanks to you again, George ; Keep up the good work!!!
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