Hello!
If anyone here has any ideas where to put a "standby" switch on a Quad II, please reply to a novice.
The idea is to shut off everything (B+?), except the heater voltage to keep the valves warm.
I saw smth here with ICs etc. (Jukka Tolonen's), but I'd rather just have a simple switch.
Thanx,
Tom
If anyone here has any ideas where to put a "standby" switch on a Quad II, please reply to a novice.
The idea is to shut off everything (B+?), except the heater voltage to keep the valves warm.
I saw smth here with ICs etc. (Jukka Tolonen's), but I'd rather just have a simple switch.
Thanx,
Tom
If your aim is simply to allow th valves to warm up longer, then a simple switch could be used, although with an indirectly-heated rectifier it's not really worth it.
You must not leave the valves on with full heater voltage for long periods; this will cause cathode-poisoning.
If you wish to leave the valves on permanently, then they must be run at about 60% of the heater voltage (i.e. about 4v).
This means that a "simple switch" will not do.
7N7
You must not leave the valves on with full heater voltage for long periods; this will cause cathode-poisoning.
If you wish to leave the valves on permanently, then they must be run at about 60% of the heater voltage (i.e. about 4v).
This means that a "simple switch" will not do.
7N7
Thanx for the replies!
I mainly thought about extending the life of the valves and also to provide a soft-start every time I bring home a new batch of NOS GEC KT66s, of course
Fdegrove, 7N7: would you please elaborate the built-in soft start in the Quad II using GZ32 (GZ34?)? How does that work?
Cheers,
Tom
I mainly thought about extending the life of the valves and also to provide a soft-start every time I bring home a new batch of NOS GEC KT66s, of course
Fdegrove, 7N7: would you please elaborate the built-in soft start in the Quad II using GZ32 (GZ34?)? How does that work?
Cheers,
Tom
Virtual Soft Start
Quad II is fitted with a rectifier valve. This is a GZ32, an indirectly-heated type. This rectifier takes perhaps 15 - 20 secs to warm up before it will pass current. The current increases as the valve warms up therefore a soft start is guaranteed.
Meanwhile all the other valves have been warming up too, and should have reached probably >80% of their operating temperatures, ergo no problem.
As I mentioned earlier, if you want to leave the valves idling, i.e. with heaters on but no HT, then you must arrange things so that they idle at about 60% of normal heater voltage.
7N7
Zombie said:Thanx for the replies!
I mainly thought about extending the life of the valves and also to provide a soft-start every time I bring home a new batch of NOS GEC KT66s, of course
Fdegrove, 7N7: would you please elaborate the built-in soft start in the Quad II using GZ32 (GZ34?)? How does that work?
Cheers,
Tom
Quad II is fitted with a rectifier valve. This is a GZ32, an indirectly-heated type. This rectifier takes perhaps 15 - 20 secs to warm up before it will pass current. The current increases as the valve warms up therefore a soft start is guaranteed.
Meanwhile all the other valves have been warming up too, and should have reached probably >80% of their operating temperatures, ergo no problem.
As I mentioned earlier, if you want to leave the valves idling, i.e. with heaters on but no HT, then you must arrange things so that they idle at about 60% of normal heater voltage.
7N7
7N7 said:
If I remember rightly, (and I admit I'm desperately trying to remember a circuit I saw 20 years ago!) it is possible to have an idling voltage for the valves by placing a half-wave rectifier (a standard silicon rectifier) in the heater leads. So long as there is no cap smoothing, the rectifier will pass half cycles at RMS voltages only, so 3.15v x 1.414 = approx 4.5v, enough to keep the valves warm without risking cathode poisoning. Then a simple switch wired across the rectifier will give the normal/idling voltage control.
The explanation may not be brilliant but the use of a half wave rectifier as a 'voltage dropper' did enjoy some success in old AC/DC radios as it meant you could reduce heat by avoiding a resistor dropper in the heater leads. It has also been used as a method of having an idling voltage on soldering irons, to keep them warm in between use and reduce warm-up time.
Hi,
As for the Quad, I would leave it as it is. There is a good chance of doing more harm than good.
Cheers,
Bournville, you may be thinking of the standard practice in the last days of valve TV's. Instead of big dropper restors, a silicon diode was fitted in series with the heater chain. In fact it gave 1/4 power (1/2V * 1/2I), and so saved on heat. The valves were actually run at full power, but there were savings in heat.
As for the Quad, I would leave it as it is. There is a good chance of doing more harm than good.
Cheers,
John,
It's a long time ago, but I have seen rectifiers used in this way - as droppers instead of resistors in the heater line on AC/DC sets and as standby on soldering irons - in a 6.3v line it will reduce the voltage to about 4.5 (so long as you don't try to smooth it!!) - you are right about the use in TVs also (easier than calculating the value of capacitor droppers!).
I personally would not use this system either, but it does provide a solution if Zombie wishes to go this route.
It's a long time ago, but I have seen rectifiers used in this way - as droppers instead of resistors in the heater line on AC/DC sets and as standby on soldering irons - in a 6.3v line it will reduce the voltage to about 4.5 (so long as you don't try to smooth it!!) - you are right about the use in TVs also (easier than calculating the value of capacitor droppers!).
I personally would not use this system either, but it does provide a solution if Zombie wishes to go this route.
Thank you all for the wealth of wisdom!
I had this discussion with another Quad II owner yesterday. So I decided to turn to the people that know...I realize that it's better to leave it as it is...
EC8010: finding batches of NOS GEC KT66 isn't that a rare event, actually.
I slowly open a door and I see shelf after shelf with those greyish-blue, blue and yellow boxes...suddenly I wake up, breathing heavily, sweating...
I had this discussion with another Quad II owner yesterday. So I decided to turn to the people that know...I realize that it's better to leave it as it is...
EC8010: finding batches of NOS GEC KT66 isn't that a rare event, actually.
I slowly open a door and I see shelf after shelf with those greyish-blue, blue and yellow boxes...suddenly I wake up, breathing heavily, sweating...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.