DIY tube preamp with 5687

[ervinl]

I would like to build 5687 tube simple pre amp as in diyparadise. Could I pump out the B+ to 500V or more (e.g. around 600V, as coupling caps limit at 630 V).

If i use 500-600 V as B+, what value, type and wattage of suggested Rp and Rk? What about the filament, should it be floating (I use DC), or should be connected to 0/GND, e.g. to pin 8?

Thanks,

Ervin L

[Arnulf]

Why ?

[alexg]

I agree with Arnulf, why that high of a B+?

[kevinkr]

The 5687 works very nicely with 100V - 200V on the plate, and probably would be rather unhappy at 500 - 600V as it is not really designed for operation at such high voltages. (Maximum rated is 330V)

Pre-amplifiers typically only need to deliver a few volts of signal to the power amplifier so these kinds of voltage levels are not required in this application.

Note that a single tube with a pair of plate to line transformers could make a very nice, simple stereo line stage.

[makaiyumtony]

Originally Posted by ervinl

I would like to build 5687 tube simple pre amp as in diyparadise. Could I pump out the B+ to 500V or more (e.g. around 600V, as coupling caps limit at 630 V).

If i use 500-600 V as B+, what value, type and wattage of suggested Rp and Rk? What about the filament, should it be floating (I use DC), or should be connected to 0/GND, e.g. to pin 8?

Thanks,

Ervin L

5687 in mu follower for pre amp, sound very good. and top voltage will be 400-450V (actually 200v for each one). low voltage high current always sound better than high voltage with less current in tube circute no matter for power amp or pre amp
regard tony ma

[tubesteve]

i am sorry, but someone who asks this question, should not consider buiding a tube (pre) amp. but he should consider to study first and then start building. looks like: how i can make a tank run 350km/h?

[bigwill]

Originally Posted by makaiyumtony

low voltage high current always sound better than high voltage with less current in tube circute no matter for power amp or pre amp
regard tony ma

Massive incorrect generalization

[dave slagle]

Originally Posted by alexg

I agree with Arnulf, why that high of a B+?

Maybe the goal is something crazy like to load the tube with 10X its internal resistance.

at 20ma the Rp is about 2K and 20ma through a 20K plate resistor will get rid of 400V of that really quickly :-)

I came up with 500VB+
20K load resistor
200 ohm cathode resistor
gives 120V P-K -3.8V bias and 18ma of current.

dave

[Arnulf]

Originally Posted by dave slagle

Maybe the goal is something crazy like to load the tube with 10X its internal resistance.

One can do that with a CCS and get better result with lower voltage so the question to OP remains: why would he want to do something as silly as that ? It is difficult to help when we don';t understand the motivation behind such weird design goal.

[makaiyumtony]

Originally Posted by bigwill

Massive incorrect generalization

try 12AX7 with 1 ma compare to WE437A in 30 ma for a same gain pre amp you will have the answer, or same tube 801' sound in 1 kv with only 10ma compare to 220 v with 90 ma the difference even bigger