Ok, it looks as if we're on the wrong track here🙁
Heck, a preamp with 10R op impedance; that'd be nice😎
I'm back in 1 hour...😉
Heck, a preamp with 10R op impedance; that'd be nice😎
I'm back in 1 hour...😉
10R may be due to the fact that my preamp uses output transformers.
Just another thing to check, this is the interstage I use: http://www.homepages.hetnet.nl/~rjonkers/interstage.jpg
A: 180V from PSU
B: To plate of 5687 tube (pin 1 and 9)
C: Grid from 300B
D: Bias -135V
parallel to C & D a 62K resistor R13.
Wired correctly?
Just another thing to check, this is the interstage I use: http://www.homepages.hetnet.nl/~rjonkers/interstage.jpg
A: 180V from PSU
B: To plate of 5687 tube (pin 1 and 9)
C: Grid from 300B
D: Bias -135V
parallel to C & D a 62K resistor R13.
Wired correctly?
Ralph,
Do you have a test CD or Audio Generator?
If not, I suggest you could download a software generator, and use your computer soundcard, or burn an audio CDR, tpo use in your CD player.
Unless anyone has any better suggestions, I intend to ask you to use your DVM on an AC range, to measure the signal voltage through the system.
__________________________________
Do you have a test CD or Audio Generator?
If not, I suggest you could download a software generator, and use your computer soundcard, or burn an audio CDR, tpo use in your CD player.
Unless anyone has any better suggestions, I intend to ask you to use your DVM on an AC range, to measure the signal voltage through the system.
__________________________________
Mmm. I was beginning to wonder.
That looks fine. Even the 62K 5%😉
I like to compensate my inexperiance by using good components 😀
John,
I have a test CD with tones from 20hz - 20khz. My multimeter can measure AC only in the 50hz - 400hz area. What is it exactly you want me to measure?
Ah, good.
Even though it says 400Hz max, that'll be for the stated accuracy. It'll probably go much higher.
Anyway, use 400Hz for now.
Please play the 400Hz track and measure the AC volts output from 1 channel of the CD player, then from the preamp at full volume, and nothing connected.
Next: Connect the amp, and measure between the grid and ground. It should be the same.
Even though it says 400Hz max, that'll be for the stated accuracy. It'll probably go much higher.
Anyway, use 400Hz for now.
Please play the 400Hz track and measure the AC volts output from 1 channel of the CD player, then from the preamp at full volume, and nothing connected.
Next: Connect the amp, and measure between the grid and ground. It should be the same.
400 hz 0db
cdplayer 1,93V
preamp out max 10,78V
Can't connect poweramp with this setting, will blow my loudspeakers and ears ... BTW with grid do you mean the 300B grid or 5687 grid?
cdplayer 1,93V
preamp out max 10,78V
Can't connect poweramp with this setting, will blow my loudspeakers and ears ... BTW with grid do you mean the 300B grid or 5687 grid?
OK.😀
I meant the 5687 grid.
BTW, now we have some voltages, let's settle on adjusting the preamp for 1volt AC signal.
And, can you check what the voltage measures at 50Hz and 10KHz please.
Had to go to -20dB because I only have 400hz @ 0dB.
400 hz -20dB 1,02V from preamp (vol max open).
400 hz -20db 0,17V from cdplayer
50hz -20db 0,18V from cdplayer
10Khz -20db 0,00 from player on DMM
connecting the pre to the power gives 1,01V - 1,03V between grid and earth ...
Maybe we should give it a rest for a day ...
400 hz -20dB 1,02V from preamp (vol max open).
400 hz -20db 0,17V from cdplayer
50hz -20db 0,18V from cdplayer
10Khz -20db 0,00 from player on DMM
connecting the pre to the power gives 1,01V - 1,03V between grid and earth ...
Maybe we should give it a rest for a day ...
OK🙂 Looks as if your DVM is "as specified". Sorry.
But at least we have read that the correct level at one frequency is geting to the first valve.
Maybe tomorrow.🙂
Cheers,
Zo.
Hi John,
For info:
My all valve preamp has an output Z of 47 Ohm, a voltage swing of 45V, THD better than 0.05% and S/N at -90dB.
Admittedly the S/N is way better than my own.😀
Cheers,😉
Hi John,
For info:
My all valve preamp has an output Z of 47 Ohm, a voltage swing of 45V, THD better than 0.05% and S/N at -90dB.
Admittedly the S/N is way better than my own.😀
Cheers,😉
Hi John,
Can't do much tonight, have to go, but have plenty time this weekend. If you point me in the direction you want me to go, I'll start Sat morning!
Thanks, Ralph
Can't do much tonight, have to go, but have plenty time this weekend. If you point me in the direction you want me to go, I'll start Sat morning!
Thanks, Ralph
Just a quick check:
http://www.homepages.hetnet.nl/~rjonkers/interstage.jpg
From A to B I measure 560 Ohms , from A to C I measure 80K.
http://www.homepages.hetnet.nl/~rjonkers/interstage.jpg
From A to B I measure 560 Ohms , from A to C I measure 80K.
If you measure 560 ohms between A - B, then you should measure ~560 ohms between C - D.
Any reading between AB and CD will be your circuit.
I'll have a look and see what it should be.😉
Any reading between AB and CD will be your circuit.
I'll have a look and see what it should be.😉
I just noticed a slight error on your schematic. It will affect your HF response (but only very slightly):
The driver transformer should be connected so that the grid connects to the bottom of the secondary.
Ie. If V4 anode connects to B, then V3 grid should connect to D.
The driver transformer should be connected so that the grid connects to the bottom of the secondary.
Ie. If V4 anode connects to B, then V3 grid should connect to D.
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