OK,
I did some experiments tonight on the subject of tying the plate and grid pins together - but I don't have a definitive answer but a good indication.
On the subject of my differing voltages readings (see post above) tying the pins together made no difference. So I traced back the voltages and found that the top valve was where the difference started - so I swapped them around and now my voltages are spot on. So the voltage problem (and hence current each side) was down to the tubes rather than the wiring/set up.
So having fixed that, and tied the pins together I do think there was a small sonic gain, principally in teh area of resolution - where there was a busy soundstage, each instrument was easier to pick out. This of course could well be due to the balancing of the tubes.
So, its probably the way to go to tie the pins together - it can't hurt.
Fran
I did some experiments tonight on the subject of tying the plate and grid pins together - but I don't have a definitive answer but a good indication.
On the subject of my differing voltages readings (see post above) tying the pins together made no difference. So I traced back the voltages and found that the top valve was where the difference started - so I swapped them around and now my voltages are spot on. So the voltage problem (and hence current each side) was down to the tubes rather than the wiring/set up.
So having fixed that, and tied the pins together I do think there was a small sonic gain, principally in teh area of resolution - where there was a busy soundstage, each instrument was easier to pick out. This of course could well be due to the balancing of the tubes.
So, its probably the way to go to tie the pins together - it can't hurt.
Fran
hi guys
Please bare with me, as this might be newbie questions, as this is my 1st tube amp diy.
i have manage to get all the components and parts to build this linestage. i have questions.
1. whats the recommended value for Rdrop for heater power supply if my power transformer 3A measured range from 6.1v to 6.3v.
2. whats the purposes of Rdrop? to drop the voltage of the PT to acceptable voltage for heater?
3. anyone try regulated for 6T4 heater? or it is not necessary?
4. i am planning of using EZ81 to rectify the voltage. would i better of has separate power transformer for EZ81 heater and 6T4? or my 3.15v CT 3A is good? if use together, will it affect the performance of 6T4, should i separate them with Rdrop? whats the recommended value?
note: my plan for power supply, modeled in PSUD
167vac/75R=>EZ81=>50uF=>25H/592R=>100uF=>1K=>220uF, gives 139vdc of B+
any comments really appreciated. thx in adv
Please bare with me, as this might be newbie questions, as this is my 1st tube amp diy.
i have manage to get all the components and parts to build this linestage. i have questions.
1. whats the recommended value for Rdrop for heater power supply if my power transformer 3A measured range from 6.1v to 6.3v.
2. whats the purposes of Rdrop? to drop the voltage of the PT to acceptable voltage for heater?
3. anyone try regulated for 6T4 heater? or it is not necessary?
4. i am planning of using EZ81 to rectify the voltage. would i better of has separate power transformer for EZ81 heater and 6T4? or my 3.15v CT 3A is good? if use together, will it affect the performance of 6T4, should i separate them with Rdrop? whats the recommended value?
note: my plan for power supply, modeled in PSUD
167vac/75R=>EZ81=>50uF=>25H/592R=>100uF=>1K=>220uF, gives 139vdc of B+
any comments really appreciated. thx in adv
Yes, Rdrop is to keep the voltage that the heaters see at, or just below, 6.3Vac. I prefer 6.1-6.2Vac. It it is determined by trial and application of Ohm's Law.
If you would like to use a regulated (and thus DC) heater supply, with its attendant cost and complexity, go ahead on; I have no objection. I will say that with my slightly filtered (see the capacitor across the heater circuit, to filter out the hi-frequency rubbish possibly coming in from the wall AC), I am getting on the average 0.03mV (thirty microvolts) of hum + noise on the output of my circuit, which seems about half tube rush. I have other more important places to spend the client's money than on this spec right now.
I do not dictate; I advise, as I think myself able.
Aloha,
Poinz
If you would like to use a regulated (and thus DC) heater supply, with its attendant cost and complexity, go ahead on; I have no objection. I will say that with my slightly filtered (see the capacitor across the heater circuit, to filter out the hi-frequency rubbish possibly coming in from the wall AC), I am getting on the average 0.03mV (thirty microvolts) of hum + noise on the output of my circuit, which seems about half tube rush. I have other more important places to spend the client's money than on this spec right now.
I do not dictate; I advise, as I think myself able.
Aloha,
Poinz
just wire 6t4 up and the voltage measures:
B+ 136vdc
Heater floats at approx 23.5V above ground
Top cathode: approx 63V
Bottom plate: approx 62.5
Bottom cathode: approx 1.4
Heater voltage: 5.9VAC
just wondering why the cathode and plate voltage is 60 plus instead of 70 plus volt as others?
thx
B+ 136vdc
Heater floats at approx 23.5V above ground
Top cathode: approx 63V
Bottom plate: approx 62.5
Bottom cathode: approx 1.4
Heater voltage: 5.9VAC
just wondering why the cathode and plate voltage is 60 plus instead of 70 plus volt as others?
thx
after more hours of running. All I can say is superb. Very open. Details on par w my solid state Pre but this 6t4 is more natural soundstage is bigger. Highly recommended. I am using LDR as pot by the way and use tube rectifier.
Move the psu section. It solve some of the hissing problem I post earlier to acceptable range. But the tubes I got is not tested and matched hence trial and error to get the right voltage parameter for cathode and plate voltage
Poinz, thx for the superb design. Just wondering if anything can be done for the volume thing so I can have wider tuning range? Thx again
Erwin
Move the psu section. It solve some of the hissing problem I post earlier to acceptable range. But the tubes I got is not tested and matched hence trial and error to get the right voltage parameter for cathode and plate voltage
Poinz, thx for the superb design. Just wondering if anything can be done for the volume thing so I can have wider tuning range? Thx again
Erwin
Milen, I can't imagine where all that hiss is coming from; 6T4 is not a noisy tube (something we worry about when using these teevee utility tubes that are not optimized for audio). My circuit is dead silent, between 20 and 30µV. Two possibilities come to mind. The first is that regulated supply - don't forget to put a high quality cap to ground between it and the circuit, fractional µF should be big enough if it's hiss. The other is that funny volume control. Test the input to the grid to see if that noise is already there.
Aloha,
Poinz
Edit: you'd think I could spell by now.
Aloha,
Poinz
Edit: you'd think I could spell by now.
Hi Poinz
thanks for the tips.
i do not use regulated psu. i am using tube rectifier EZ81 (or maybe this tube that hiss) i might change the tube then. and filament ac of 5.8vac (too low.. maybe not pure enough tranformer winding=guessing)
the LDR pot i am using suppose to be dead silent. as i am using the same thing on my solid state pre and its dead silent. but i will double check.
i am using sikorel 125 (no idea hows the quality, its NOS, but i think sikorel shouldnt be too bad though) parallel few caps to get the required capacitance.
or do you suggest regulated psu for heater to solve the hissing?
do you found 6t4 tubes to be varies in quality? i got 5 RCA and 5 GE. test them all and cant get the voltage to balance between left and right channel. they also have different load that cause the B+ to varies between tubes (or they need to run in 1st to stabilized ?). i am using RCA to the B+ and GE to the ground.
one more thing, anyway to lower the gain? as i suspect my system gain is too much for driving my 100w amp, which later will be replace by smaller watt amp/ Class A.
PS: great stuff Poinz, maloha for the schematic. really nice preamp. very open sound and details. soundstage is scarily huge. very natural. best that i heard till now.
Erwin
thanks for the tips.
i do not use regulated psu. i am using tube rectifier EZ81 (or maybe this tube that hiss) i might change the tube then. and filament ac of 5.8vac (too low.. maybe not pure enough tranformer winding=guessing)
the LDR pot i am using suppose to be dead silent. as i am using the same thing on my solid state pre and its dead silent. but i will double check.
i am using sikorel 125 (no idea hows the quality, its NOS, but i think sikorel shouldnt be too bad though) parallel few caps to get the required capacitance.
or do you suggest regulated psu for heater to solve the hissing?
do you found 6t4 tubes to be varies in quality? i got 5 RCA and 5 GE. test them all and cant get the voltage to balance between left and right channel. they also have different load that cause the B+ to varies between tubes (or they need to run in 1st to stabilized ?). i am using RCA to the B+ and GE to the ground.
one more thing, anyway to lower the gain? as i suspect my system gain is too much for driving my 100w amp, which later will be replace by smaller watt amp/ Class A.
PS: great stuff Poinz, maloha for the schematic. really nice preamp. very open sound and details. soundstage is scarily huge. very natural. best that i heard till now.
Erwin
hi poinz
has been reading about the voltage devider.
will i be able to lower the gain by reducing the resistor to the ground at the output? for instance to 9K? not sure if this work.. but voltage devider always work with 2 resistor.
or add 1K resistor in series at output?
thanks in adv.
regards,
Erwin
has been reading about the voltage devider.
will i be able to lower the gain by reducing the resistor to the ground at the output? for instance to 9K? not sure if this work.. but voltage devider always work with 2 resistor.
or add 1K resistor in series at output?
thanks in adv.
regards,
Erwin
hi guys
i change the tube to balance out the right and left channel.. i got
B+ 136vdc
Heater floats at approx 23.5V above ground
Top cathode: approx 103V
Bottom plate: approx 101
Bottom cathode: approx 0.9
Heater voltage: 5.9VAC
the circuit only draw 22mA both channel... what do you guys have?
as before the dropping resistor is 174v, after 1.5K the voltage become 140vdc
suggestion? but it still sound good tho but hiss louder.
i got other tube that have the top cathode 63v. forget to measure the current. which is better?
regards,
Erwin
i change the tube to balance out the right and left channel.. i got
B+ 136vdc
Heater floats at approx 23.5V above ground
Top cathode: approx 103V
Bottom plate: approx 101
Bottom cathode: approx 0.9
Heater voltage: 5.9VAC
the circuit only draw 22mA both channel... what do you guys have?
as before the dropping resistor is 174v, after 1.5K the voltage become 140vdc
suggestion? but it still sound good tho but hiss louder.
i got other tube that have the top cathode 63v. forget to measure the current. which is better?
regards,
Erwin
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