0.036 A includes both plate and g2 current, therefore the real plate dissipation at idle is just a bit lower than 10.9872
@calpe, you have a Sovtek EL84. max plate dissipation is 14W, not 12W like the original EL84.
Congratulations! You (and your friends here) persevered and I expect we all learned some things along the way. Thanks for making us part of your journey.
A new SPP is brought into the world. It will serve you very well for a long time, and you heirs may enjoy it long after you.
Down the road when the improvement itch hits, read up on Dave Gillespie’s EFB circuit and, consider installing it instead of your 300 Ohm cathode resistors. http://www.tronola.com/A_New_Look_At_An_Old_Friend.pdf. I have installed EFB in several amplifiers and it provides an improvement one could measure and easily hear.
P.S. Let us know how things are progressing and some comments about how your SPP sounds to you. If needed we could help figure out the specifications of the resistor to install parallel to R1.
Post 483....😉 sorry OldHector.
I'll read the Dave Gillespie’s EFB circuit, but initially i'll probably leave the build as it is, that's way over my head.
Ok, so with a very small amount of resistors i have, measuring: -
150R & 2K2 = 146R
150R & 1K = 135R
150R & 560R = 122R
I'll need to keep the 150R for protection, in case the other parallel goes open circuit.
A couple of more tests...
I'll read the Dave Gillespie’s EFB circuit, but initially i'll probably leave the build as it is, that's way over my head.
Ok, so with a very small amount of resistors i have, measuring: -
150R & 2K2 = 146R
150R & 1K = 135R
150R & 560R = 122R
I'll need to keep the 150R for protection, in case the other parallel goes open circuit.
A couple of more tests...
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Francois, as you know on the original build by G.Anderson of Tubelabs R1 was a 150R 5W.
On a quick test i did earlier the resistors were running warm, so i prefer to stick to 5W, just for safety.
On a quick test i did earlier the resistors were running warm, so i prefer to stick to 5W, just for safety.
Hello All,
I have been following this thread since purchasing a Tubelab SPP board and all the bits from a kind gentleman. I have a pair of output transformers from an old Fisher X-202 which means that I can't follow the ultra-linear configuration shown in the excellent schematic drawn by Ian444 and annotated by others. (I only have three wires at the primary.) I believe this means I have to use a pentode configuration and I am wondering if anyone would be able to provide a schematic for such a beast. I think this entails feeding B+ to pin 9 on the EL84s... I am assuming that I can't just split the two anode feeds and connect to pin 9 to preserve the UL configuration.
Any and all help/suggestions would be greatly appreciated, as this is my first build. (As is obvious, I imagine.)
Thanks very much,
Andrew
PS Bought a much-maligned JJ 5AR4 because of this article: https://sonoboom.com/5ar4-rectifier-tubes-gz34/
I have been following this thread since purchasing a Tubelab SPP board and all the bits from a kind gentleman. I have a pair of output transformers from an old Fisher X-202 which means that I can't follow the ultra-linear configuration shown in the excellent schematic drawn by Ian444 and annotated by others. (I only have three wires at the primary.) I believe this means I have to use a pentode configuration and I am wondering if anyone would be able to provide a schematic for such a beast. I think this entails feeding B+ to pin 9 on the EL84s... I am assuming that I can't just split the two anode feeds and connect to pin 9 to preserve the UL configuration.
Any and all help/suggestions would be greatly appreciated, as this is my first build. (As is obvious, I imagine.)
Thanks very much,
Andrew
PS Bought a much-maligned JJ 5AR4 because of this article: https://sonoboom.com/5ar4-rectifier-tubes-gz34/
(I hope OP is OK with diverting the thread from his personal build, to a general “first time builder” thread. If not you could start your own thread)
Welcome as a first time builder. Your Fisher X-202 outputs are excellent, congratulations, but with a primary impedance of 6600 Ohm they are more suited to amplifiers using 7591, or 6L6-type output tubes.
Read here about these “fabled transformers” https://audiokarma.org/forums/index.php?threads/fisher-x-200-kx-200-design-notes.654228/
Doesn’t mean they can’t be used for EL84 amps, but with such special transformers it is advised to use tubes that bring out the best of them. How you could proceed depends a lot on your power transformer. Could you tell us more about that?
You are correct that the X-202 transformers are not UL and will require a power supply for the screen grids. It could be as simple a connecting B+ directly to the screens, or it could be more elaborate. As you may have read in the Tubelabs assembly manual, the SPP PCB is purposely made so that you could easily use it for non-UL connected amps, if your transformers require it.
The non-UL scheme could also have an additional RC filter and most “Golden age“ designs favored a reduced screen supply voltage of around 75% of B+. An example is this Harmon Kardon: https://www.audiokarma.org/forums/i...cted-schematic-and-restoration-photos.270846/ (Further improvement is an LC stage, a choke instead of a resistor, has distinct advantage).
The best approach is having a screen supply that “follows” B+, but does not restrict the supply, because on peaks the screen supply rises dramatically. This could cause RC supplies to “starve” the screen when it needs the electrons most. That is the objective of Dave Gillespie’s EFBII approach, that uses a MOSFET to modulate the screen supply in a fixed ratio with B+ (usually 75%). This together with the EFB that also modulates the fixed bias of the power tubes, I believe, is the best one could do with X-202 output transformers and if you are adventurous you could too.
See scan0001 for the EFBII supply, and scan0004 for the schematic: https://audiokarma.org/forums/index.php?threads/improving-the-fisher-400.511867/page-4#post-6686863
If you definitely want use the Tubelab SPP PCB, you could do so and still do EFB. I’m using the PCB with very minor/easy modification to build a 6P15P amplifier that is EFB biased and adjustable screen supply, but you could do the same for 6P14P/EL84.
So, you have many paths forward. One final consideration is to sell your X-202 transformers and buy a pair perfect for the EL84 SPP. Or you could build the EL86 version of the SPP and use your x-202 transformer at 3300 ohm primary impedance by connecting your 8 Ohm speakers to the 16 Ohm transformer secondaries.
Good luck and keep us informed.
Welcome as a first time builder. Your Fisher X-202 outputs are excellent, congratulations, but with a primary impedance of 6600 Ohm they are more suited to amplifiers using 7591, or 6L6-type output tubes.
Read here about these “fabled transformers” https://audiokarma.org/forums/index.php?threads/fisher-x-200-kx-200-design-notes.654228/
Doesn’t mean they can’t be used for EL84 amps, but with such special transformers it is advised to use tubes that bring out the best of them. How you could proceed depends a lot on your power transformer. Could you tell us more about that?
You are correct that the X-202 transformers are not UL and will require a power supply for the screen grids. It could be as simple a connecting B+ directly to the screens, or it could be more elaborate. As you may have read in the Tubelabs assembly manual, the SPP PCB is purposely made so that you could easily use it for non-UL connected amps, if your transformers require it.
The non-UL scheme could also have an additional RC filter and most “Golden age“ designs favored a reduced screen supply voltage of around 75% of B+. An example is this Harmon Kardon: https://www.audiokarma.org/forums/i...cted-schematic-and-restoration-photos.270846/ (Further improvement is an LC stage, a choke instead of a resistor, has distinct advantage).
The best approach is having a screen supply that “follows” B+, but does not restrict the supply, because on peaks the screen supply rises dramatically. This could cause RC supplies to “starve” the screen when it needs the electrons most. That is the objective of Dave Gillespie’s EFBII approach, that uses a MOSFET to modulate the screen supply in a fixed ratio with B+ (usually 75%). This together with the EFB that also modulates the fixed bias of the power tubes, I believe, is the best one could do with X-202 output transformers and if you are adventurous you could too.
See scan0001 for the EFBII supply, and scan0004 for the schematic: https://audiokarma.org/forums/index.php?threads/improving-the-fisher-400.511867/page-4#post-6686863
If you definitely want use the Tubelab SPP PCB, you could do so and still do EFB. I’m using the PCB with very minor/easy modification to build a 6P15P amplifier that is EFB biased and adjustable screen supply, but you could do the same for 6P14P/EL84.
So, you have many paths forward. One final consideration is to sell your X-202 transformers and buy a pair perfect for the EL84 SPP. Or you could build the EL86 version of the SPP and use your x-202 transformer at 3300 ohm primary impedance by connecting your 8 Ohm speakers to the 16 Ohm transformer secondaries.
Good luck and keep us informed.
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The 7189 tubes are Beam Pentodes (They have Beam Formers; they do Not have a suppressor grid).
The 7189 is sort of a higher voltage version of both the 6BQ5 Beam Power tube (beam formers), and the EL84 Pentode (suppressor grid).
Except for the larger maximum plate and screen voltages of the 7189, both the 6BQ5 and EL84 are very similarly specified.
Since your output transformers do not have the Ultra Linear Taps, you have 2 options:
1. As mentioned above, use the 7189s in Beam Pentode mode (Beam Power mode).
Or,
2. You could use the 7189s in Triode Wired Mode (very simple to wire that way). A 100 Ohm resistor from the screen to the same tube's plate does the trick (instead of connecting the screen to an Ultra linear tap, often done with the same 100 Ohm resistor).
This is one modification that is not hard to do, even when you use PCBs. No need to cut traces; just leave the PCB to UL tap unwired; and connect a 100 Ohm resistor right on the bottom of the board from plate to screen.
Triode wired 7189s will have less power than Ultra Linear mode, but can be used without any global negative feedback.
The plate impedance, rp, in triode mode is about 1/2 of the plate impedance of Ultra Linear mode.
Try connecting 6 Ohm or 4 Ohm loudspeakers on the 4 Ohm output tap, 8 Ohm loudspeakers on the 8 Ohm or the 4 Ohm tap.
Have fun building and listening!
The 7189 is sort of a higher voltage version of both the 6BQ5 Beam Power tube (beam formers), and the EL84 Pentode (suppressor grid).
Except for the larger maximum plate and screen voltages of the 7189, both the 6BQ5 and EL84 are very similarly specified.
Since your output transformers do not have the Ultra Linear Taps, you have 2 options:
1. As mentioned above, use the 7189s in Beam Pentode mode (Beam Power mode).
Or,
2. You could use the 7189s in Triode Wired Mode (very simple to wire that way). A 100 Ohm resistor from the screen to the same tube's plate does the trick (instead of connecting the screen to an Ultra linear tap, often done with the same 100 Ohm resistor).
This is one modification that is not hard to do, even when you use PCBs. No need to cut traces; just leave the PCB to UL tap unwired; and connect a 100 Ohm resistor right on the bottom of the board from plate to screen.
Triode wired 7189s will have less power than Ultra Linear mode, but can be used without any global negative feedback.
The plate impedance, rp, in triode mode is about 1/2 of the plate impedance of Ultra Linear mode.
Try connecting 6 Ohm or 4 Ohm loudspeakers on the 4 Ohm output tap, 8 Ohm loudspeakers on the 8 Ohm or the 4 Ohm tap.
Have fun building and listening!
Hi Andrew, lots of excellent advice above. If this is your first foray into building any amplifier then I think it pays to stick to the stock parts, and then look at adapting to fit different parts when you have a working baseline. You live in Hammond country by the looks of yor flag - are a pair of OPTs suitable for EL84s with UL taps out of te question?
PLEASE START A NEW THREAD FOR YOUR BUILD SO WE DO NOT MIX MY BUILD WITH YOUR BUILD.
PLEASE AVOID REPLYING TO ATJBLACK SO THAT HE STARTS A NEW BUILD
If we were following Forum etiquette I think both of you should be posting on the Tubelab forum, once you got beyond the 'what shall I build with these?' questions.
On that forum there is a single thread that covers all the historical issues of builders of the Tubelab SPP.
Tubelab SPP
The aim has to be the minimum repetition of the same questions so that the threads are resources for future builders.
On that forum there is a single thread that covers all the historical issues of builders of the Tubelab SPP.
Tubelab SPP
The aim has to be the minimum repetition of the same questions so that the threads are resources for future builders.
I'd rather we stick to the thread i began and not mix a different build.
Post #493, 7 left for to reach 500 😉😉
Historical issues perhaps would apply to those that used e.g. Hammond Tx's etc., so i suggest that other thread to others, if not start a new thread.
As we know this build from my own choice is with the U.K. Primary Winding Transformers.
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Chill a bit guys. If a thread takes a bit of a diversion we might learn something we wouldn't have otherwise.
S.
S.
Sorry to have posted against etiquette. I took the title of the thread to refer to first time builds in general, rather than to a specific build. Thanks very much, nevertheless, to those who took the time to share their expertise with me (and with all of us). Your generosity is greatly appreciated.
Andrew
Andrew
Just some voltage measurements i carried out yesterday.
With Choke still in place, i have been checking with various resistor values for R1, having two resistors placed in parallel.
150R + 2K2 = 144R - B+ 315v Cathode voltage 11v Watts = 11.126
150R + 1K = 135R - B+ 319v Cathode voltage 11.18v Watts = 11.481
150R + 560R = 122R - B+ 323v Cathode voltage 11.33v Watts = 11.749
As jcalvarez mention in his post #481
"you have a Sovtek EL84. max plate dissipation is 14W, not 12W like the original EL84."
Will be allocating a small veroboard for the two parallel resistors and to ensure all cabling is tucked well away.
I'll be carrying out audio tests as from Monday, now the B+ has been sorted, thanks to all the input.
With Choke still in place, i have been checking with various resistor values for R1, having two resistors placed in parallel.
150R + 2K2 = 144R - B+ 315v Cathode voltage 11v Watts = 11.126
150R + 1K = 135R - B+ 319v Cathode voltage 11.18v Watts = 11.481
150R + 560R = 122R - B+ 323v Cathode voltage 11.33v Watts = 11.749
As jcalvarez mention in his post #481
"you have a Sovtek EL84. max plate dissipation is 14W, not 12W like the original EL84."
Will be allocating a small veroboard for the two parallel resistors and to ensure all cabling is tucked well away.
I'll be carrying out audio tests as from Monday, now the B+ has been sorted, thanks to all the input.
Looks like a good operating point. (Is that the average of the four EL84Ms?)
Keep in mind that you are calculating the combined dissipation of plate and screen, when using the cathode voltage method. The combined screen plus plate dissipation of your Sovtek EL84M/6P14P-ev is more than 14 watts and you could increase the B+ a bit further, if you wanted to maximize power. (Maximizing power will reduce power tube life somewhat).
However, do your testing and listening before increasing B+ further. I think you are at a good operation point with the 560R in parallel with R1. That will also allow you to use “regular” EL84s in stead of the uprated EL84Ms without worry.
Francois, the valves are `the normal EL84's not the EL84M's.
Don't intend to push this amp to the limits, so i'll play with B+ and check the audio as from Monday, but i'll probably aim at a B+ of : -
R1 150R + 560R = 122R
B+ 323v
Cathode voltage 11.33v
Watts = 11.749
Sounds good! (Pun intended). 😁 And hurrah! We just made #500!
Check your EL84 screen dissipation at your final operating conditions before buttoning up everything. (Measure the voltage across the 100R screen resistors (R113, 117), calculate the screen current and multiply that with the voltage from the screen to the top of cathode. Should be well below 1 watt)
Check your EL84 screen dissipation at your final operating conditions before buttoning up everything. (Measure the voltage across the 100R screen resistors (R113, 117), calculate the screen current and multiply that with the voltage from the screen to the top of cathode. Should be well below 1 watt)
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