News:
June 27, 2022, 11:43:34 AM

Author Topic: C/4s original SEX ,voltage questions.  (Read 10006 times)

0 Members and 1 Guest are viewing this topic.

Offline najo49

  • Full Member
  • ***
  • Posts: 169
C/4s original SEX ,voltage questions.
« on: September 04, 2012, 05:18:48 AM »
Hi I just put a set of the c4s boards in (I built them up myself). i have many of the Brainiac changes to the circut as well. I am getting just 200 v going in to the board and 116 going out. I plays fine,the voltage in the old valve mag says a considerable larger voltage. the 1k resistor is removed in the PS. Any thoughts,this may take paul or doc to comment. Thanks
Jann Olsen, [email protected]  Lowther medallion 2 with pm2a./ extended foreplay lll,/EROS phono /Grado ref/ SOTA star Vacuum SME V, /  45 amp direct coupled,c4s,mQ nickel  / paramour  2a3 w MQ iron /Original SEX monos /Jena Cables /heathkit wm6a/ proAc Tablette 50 sig , with push pull

Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5454
Re: C/4s original SEX ,voltage questions.
« Reply #1 on: September 04, 2012, 05:39:22 AM »
Unfortunately, I can't locate any information on the C4S installation and my memory does not include any details either. Do you have a manual or circuit?

The voltages ae quite acceptable, however. I would speculate that there is a series resistor between the power supply and the C4S input, which drops a substantial voltage. But changing that, and thus changing the input voltage, won't change the plate output voltage, so it won't affect the performance.
Paul Joppa

Offline najo49

  • Full Member
  • ***
  • Posts: 169
Re: C/4s original SEX ,voltage questions.
« Reply #2 on: September 06, 2012, 07:33:02 AM »
Thanks Paul, I did all the work according to the Valve schematic,and docs schematic on the c4s board. In that he says there was 300 V going in .  then  a resistor 60 ohm,then the 2907 ,350 b and and a 60k resistor to gnd. after the leds. but I only have 190 going in not 300v. But as you say ,and the fact it works fine may be I should just consider it a success,and for get about it. The rest of the mods were done according to a valve piece you wrote on SEX changes in valve. In fact the original schematic contains no voltages ,if I had them, perhaps I could have figured this out. Thanks again, let me know if you have any further thoughts. I love these amps,but i thinks i am pretty much alone in this, I guess all the bottleheads did this 16 years ago and have moved on. Jan
Jann Olsen, [email protected]  Lowther medallion 2 with pm2a./ extended foreplay lll,/EROS phono /Grado ref/ SOTA star Vacuum SME V, /  45 amp direct coupled,c4s,mQ nickel  / paramour  2a3 w MQ iron /Original SEX monos /Jena Cables /heathkit wm6a/ proAc Tablette 50 sig , with push pull

Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5454
Re: C/4s original SEX ,voltage questions.
« Reply #3 on: September 06, 2012, 05:11:07 PM »
If you tell me what issue of VALVE has the C4S schematic, I'll look it up and estimate the voltages. If you can find Doc's post of a schemo, I'll look at that too. There is probably some reason fro the 190 volts!
Paul Joppa

Offline najo49

  • Full Member
  • ***
  • Posts: 169
Re: C/4s original SEX ,voltage questions.
« Reply #4 on: September 06, 2012, 06:41:18 PM »
Paul, It was in vol. 6 no. 1. Jan
Jann Olsen, [email protected]  Lowther medallion 2 with pm2a./ extended foreplay lll,/EROS phono /Grado ref/ SOTA star Vacuum SME V, /  45 amp direct coupled,c4s,mQ nickel  / paramour  2a3 w MQ iron /Original SEX monos /Jena Cables /heathkit wm6a/ proAc Tablette 50 sig , with push pull

Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5454
Re: C/4s original SEX ,voltage questions.
« Reply #5 on: September 07, 2012, 06:08:38 AM »
OK, thanks. If you look at the schematic again, you will see a 6K resistor between the 410v and the 300v. You probably don't have 410v at the hot end of that resistor, or else that resistor is not actually 6K. Once we know which of those possibilities is correct, we can look for ways to fix it.
Paul Joppa

Offline najo49

  • Full Member
  • ***
  • Posts: 169
Re: C/4s original SEX ,voltage questions.
« Reply #6 on: September 07, 2012, 10:22:09 AM »
Paul, I  have the original 1k wirewound removed ,I have the higher47uf cap in and no 6k resistor. I have 124v going into the c4s and  116 going out. Let me know what you think. jan
Jann Olsen, [email protected]  Lowther medallion 2 with pm2a./ extended foreplay lll,/EROS phono /Grado ref/ SOTA star Vacuum SME V, /  45 amp direct coupled,c4s,mQ nickel  / paramour  2a3 w MQ iron /Original SEX monos /Jena Cables /heathkit wm6a/ proAc Tablette 50 sig , with push pull

Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5454
Re: C/4s original SEX ,voltage questions.
« Reply #7 on: September 07, 2012, 03:19:49 PM »
So, are you saying that the high voltage is now 124v instead of the normal 410 volts? And that it was 200volts a couple days ago? If so, obviously something is seriously wrong, and it has nothing to do with the C4S installation!

There were several versions of the original S.E.X. amp, I have only one version of the manual, and yours is modified anyhow. So instead of the manual voltage checks, how about these voltages:

AC filament voltage on the 6DN7s (pin 7 to pin 8) - should be close to 6.3 volts

AC high voltage transformer - from ground to the leads that go directly to the rectifier diodes - should be around 350v

DC power supply voltage, relative to ground and measured at the positive terminals of the PSU capacitors - should be over 410 volts

Tube voltages, relative to ground and at pins 1-2-3-4-5-6

These should give us a good understanding of what is going on. Believe me, if your earlier voltages are correct, then when we get this puppy working right you will be amazed at how much better it sounds!
Paul Joppa

Offline najo49

  • Full Member
  • ***
  • Posts: 169
Re: C/4s original SEX ,voltage questions.
« Reply #8 on: September 07, 2012, 04:24:02 PM »
Paul, That last post was not accurate and was miss leading. My high voltage is 453 and filliments are  6.3. I have no voltage dropping resistor where there is shown a 6k in docs c4s valve article . My voltage is however 124 going into the boards. If I disconnect the input lead to c4s the voltage at that terminal where that lead goes to is 190. after the second ps filter the 47uf one there are not any resistors. So it seems to me I should put 6k 3w right after the 47uf cap. I hope this makes more sense.jan
Jann Olsen, [email protected]  Lowther medallion 2 with pm2a./ extended foreplay lll,/EROS phono /Grado ref/ SOTA star Vacuum SME V, /  45 amp direct coupled,c4s,mQ nickel  / paramour  2a3 w MQ iron /Original SEX monos /Jena Cables /heathkit wm6a/ proAc Tablette 50 sig , with push pull

Offline najo49

  • Full Member
  • ***
  • Posts: 169
Re: C/4s original SEX ,voltage questions.
« Reply #9 on: September 08, 2012, 06:49:02 AM »
Paul here are the voltages at each pin first the valve with the input from RCA.or the left one with power cord away from you. 9.3v,425,15.5,0,109,3.14,125,125 the other tube is  9.7,424,15,84,425,132,125,125   Jan.
Jann Olsen, [email protected]  Lowther medallion 2 with pm2a./ extended foreplay lll,/EROS phono /Grado ref/ SOTA star Vacuum SME V, /  45 amp direct coupled,c4s,mQ nickel  / paramour  2a3 w MQ iron /Original SEX monos /Jena Cables /heathkit wm6a/ proAc Tablette 50 sig , with push pull

Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5454
Re: C/4s original SEX ,voltage questions.
« Reply #10 on: September 08, 2012, 10:32:40 AM »
Thanks, that helps a lot.

You do not have the circuit wired as in the VALVE circuit. The driver triode sections (pins 4, 5, and 6) are still connected as a mu follower (the original SEX circuit), but in the VALVE circuit those two sections are in parallel. You also do not have the C4S connected to a third (new) RC filter, consisting of a 6K/3W resistor and a new 47uF/450v capacitor. I suspect the C4S is connected to midpoint of the mu follower circuit, rather than the new filter off the main high voltage power supply. Finally, you report around 9v at teh power section grids (pin 1) but I suspect that is 9mV, i.e. 0.009 volts.

A couple things to watch out for here:

1) the 6DN7 sections are connected backwards from what everyone thinks - section 1 is pins 4-5-6, section 2 is pins 1-2-3.   

2) The old C4S boards are very confusing and counter-intuitive as to which resistors are in series and which are in parallel.

Those of us who were around back then have, I believe, all made the above mistakes. I know I have! Hence the reminder.
Paul Joppa

Offline najo49

  • Full Member
  • ***
  • Posts: 169
Re: C/4s original SEX ,voltage questions.
« Reply #11 on: September 09, 2012, 07:30:51 AM »
Paul, Thanks soooo much. A little more info. I have the 47uf cap installed,but as I said no 6k resistor.after the 47u the high voltage supply splits one to red transformer lead, the other then goes thru a 270k resistor to  pins 8,7,6 each lead has a resistor before connection at the above mentioned pins. On the other tube I have 2 LEDs connected to pin 4. c4s to pin 5. The connection to pin 5 was a 12k. resistor which I removed and put the c4s in its place. I will now try to get things connected as you say, Is adding the 9v battery  supply worth doing? i am also buying a set of tfa 204s from mike. considering all the transformer available today is that still the best choice? Thanks again, for sharing your infinite wisdom.
Jann Olsen, [email protected]  Lowther medallion 2 with pm2a./ extended foreplay lll,/EROS phono /Grado ref/ SOTA star Vacuum SME V, /  45 amp direct coupled,c4s,mQ nickel  / paramour  2a3 w MQ iron /Original SEX monos /Jena Cables /heathkit wm6a/ proAc Tablette 50 sig , with push pull

Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5454
Re: C/4s original SEX ,voltage questions.
« Reply #12 on: September 09, 2012, 02:43:54 PM »
Wow - this is getting more interesting, and more complicated, by the minute! An interesting historical puzzle for sure! Yes, the TFA-204 is still one of the best available. I assume you are getting the TFA-204 series feed transformer, not the TFA-2004 parallel feed version.

I now have the following references:

1) My own original SEX manual, version 1.1, 1996.

2) My article "Braniac's S.E.X. Changes, VALVE v.4 no.10 October 1997 pp. 15-16

3) The circuit "ActiveS.E.X. from VALVE v.6 no. 1 1999 p. 13 which depicts an amp converted to parallel feed and with a C4S plate load on the driver, and also incorporating some of the ideas from 2)

The circuit 3) is the most recent, however it does not include a power supply circuit, and it depicts the parallel feed mod (called ParaS.E.X.) which is different from the TFA-204 mod. Here are some notes to make sense of all this:

Power supply: The original in 1) was a CLC (10uF/10henries/10uF) followed by a series 1K power resistor. The modification described in 3) is to replace the last 10uF with 47uF450v and remove the 1K resistor (replace it with wire). This will give about 410v at the output plates.

The same circuit 3) shows a 6Kohm, 3Watt resistor and a second 47uF 450v capacitor; this is a decoupling network for the driver stage, which drops the voltage to a safe level (300v) for the C4S transistor. Notice this - there are TWO 47uF/450v capacitors per channel.

The power supply in 1) also shows a voltage divider of 270K and 100K, with a 0.1uF capacitor across the 100K. The hot end of the 270K goes to the power supply 410v, the common point where  the two resistors meet goes to pin 8 of the tubes, and the other end of the 100K goes to ground. I would suggest reducing teh 100K to around 50K; the higher value was only needed with the original driver circuit. You can put a second 100K in parallel with the existing one to get 50K.

Finally, the 6.3v winding goes to pin B7 and B8 with a twisted pair. Another twisted pair connects B7 to A7, and B8 to A8.

Output stage: This is pins 1, 2, and 3 of the tubes. They are in parallel - A1 is connected to B1, A2 to B2, and A3 to B3. In the circuit 3) the cathodes (A3/B3) are connected to the old output transformer but for the TFA-204 they should connect to a 390 ohm resistor whose other end is grounded. The circuit 3) shows that to be a 390 ohm 2 watt resistor but for the TFA-204 I recommend a 5 watt resistor. This resistor is bypassed with a 220uF 35v electrolytic, as shown in 3).

The grids (A1/B1) goes to ground through a 270K resistor, and to the driver through a 0.47uF capacitor. I recommend a small grid stopper, 200 to 500 ohms metal film, connected right at each socket pin 1, with the other wires to pin 1 going to the other end of the stopper resistor.

The plates (A2/B2) are shown in 3) going to the old output transformer and a parafeed capacitor. For the TFA-204, the plates should go to the blue output transformer wire. The red output transformer wire goes to the power supply 410v point.

Driver stage: The driver triodes are pins 4, 5, and 6. They are in parallel, same as the power section A4 connected to B4, A5 to B5, and A6 to B6. The grid (A4/B4) goes to the input RCA jack as usual.

The cathode (A6/B6) goes to ground through a 500 ohm resistor. Circuit 3) shows 1000 ohms, which is incorrect. The 500 ohms resistor must be rated at least 1/2 watt; I would use a 1 watt myself. It can be any value from 470 to 500 ohms. It is bypassed with a 220uF or greater capacitor rated 16 to 35 volts.

The C4S input comes from the second 47uF capacitor, about 300volts. The C4S output goes to the plate (A5/B5) and from there to the 0.47uF coupling capacitor. The C4S has a ground lead to signal ground as well. Note that the C4S has three 50K 1W resistors in series from the LED string to ground; this is an unusual arrangement so be sure you have it correct.
Paul Joppa

Offline najo49

  • Full Member
  • ***
  • Posts: 169
Re: C/4s original SEX ,voltage questions.
« Reply #13 on: September 11, 2012, 06:49:16 AM »
paul, I can not thank you enough for taking the time to post all this for me. everything is clear to me . I think the most misleading for me was the difference between the original schematic posted in valve and the ,version in your 3. last version which I did not have available to me. My amp pretty much was spot on for that version, except for input which is not paralel wired.,The the key was your explaining that there should be 2 47uf caps, a 47uf and a 6k  line to the c4s from the 410v.  Thanks again for your willingness to share with others ,but before we end this two more questions, they may be stupid, but I do not understand the second chock,if it is one, which is mounted on top. My understanding is the the small tranny inside connected to output is the opt. or is this a plate chock?, or the parasex opt and my old tranny  wired as a plate chock? but  the tranny on top has 4 leads to it and this is not like a simple chock but looks more like an a opt to me. I am wondering if I have a tfa 204 already or a parafeed ,or a different opt transformer  Further it does not show up on the schematic at all,except in the vol 6 no 1 c4s schematic, which makes me ask this question. ???. and lastly would the 9v battery mod be worth doing?
« Last Edit: September 11, 2012, 08:08:04 AM by najo49 »
Jann Olsen, [email protected]  Lowther medallion 2 with pm2a./ extended foreplay lll,/EROS phono /Grado ref/ SOTA star Vacuum SME V, /  45 amp direct coupled,c4s,mQ nickel  / paramour  2a3 w MQ iron /Original SEX monos /Jena Cables /heathkit wm6a/ proAc Tablette 50 sig , with push pull

Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5454
Re: C/4s original SEX ,voltage questions.
« Reply #14 on: September 11, 2012, 01:07:20 PM »
In reverse order ... the 9-v battery is a revision of the mu follower - the original input circuit It was to bias the top triode, which acts as a current source. When you install the C4S, it replaces that part of the circuit, so you take that extra triode and put it in parallel with the original first triode to get more drive current. Thus, teh 9-v thing has no place in teh C4S driver circuit.

Now, then reference 3) circuit shows the parallel feed version of the original S.E.X. The original output transformer (on top, with four wires) is re-purposed as a plate choke, with the secondary wired in the cathode as a cathode feedback. It's not a lot of feedback, only 10% of the primary winding, but it does make a difference. The small transformer with many wires is the output transformer - it can be small because it handles only the audio signal, while the plate choke handles all the DC current.

The TFA-204 is large, black, and has bell ends. The core is about 2.7" tall, 2.2" wide, and the core is 1.75" thick. It also has six wires - red and blue are the primary, black is the output ground, and yellow-orange-brown are the output taps for speakers. I don't remember which is 4, 8, or 16 ohms - when the transformers arrive they will have some notes. To install it you would remove both the 4-wire transformer/choke on top and the small output transformer underneath. The chassis plate already has the requisite four holes to mount the TFA-204 on top.
Paul Joppa