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Netzteil so in Ordnung?

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Afrobusch:
Hallo!

Blöde frage zur Bias-Sektion auf Dirk's pdf:
Die Biasspannung wird an den Schleifern abgegriffen, oder?
Und das funktioniert so für 4 Röhren(oder Röhrenpaare, whatever)?
Hätte das nämlich für jede Röhre extra eingeplant, aber so würde
ich mir einiges ersparen...

Grüße
Mathias

Dirk:
Hallo,

ja, die Spannung wird am Schleifer abgegrifen und ist für 4 Endröhren ausgelegt. Du kannst das natürlich auch anders verschalten z.B. ein Poti für zwei Röhren oder ein Poti für alle Röhren usw. Ist alles nur als Basis bzw. Beispiel gedacht, aber auch diese Bias-Einstellung findet in der Praxis Anwendung, spricht funktioniert  ;D

Gruß, Dirk

MetalBasti:
Moin,

Was haltet ihr eigentlich von dieser Variante?
Wenn man nen dicken Transistor (NE5033) wählt könnten man locker auch die Endröhren mit DC heizen :)) Eine Nummer kleiner tut es natürlich auch. Aber auch hier muss gekühlt werden.

Gruß Basti

Edit: Es muß natürlich der 2N3055 sein :)

Passenger:
Hi folks,

When considering DC heater supply one needs to consider a few things. A regulator like 78XX series need an input voltage that is at least 3 Volts higher than its output voltage. For 7806 this is 9 Volt. So the lowest voltage over the charge elco, just before the diodes start conduction again, must be 9 Volt too. A diode bridge consumes at least 1.5 Volt. To get a good DC heatersupply, at least half of the time the sinewave of the secondary voltage must be above 10.5 Volt. A 6.3 Volt AC winding has a peak voltage of 8.8 Volt and is not enough for this application. If the input voltage of a 78XX regulator gets to low, its output voltage will drop aswell and this could be the cause of having humm with a DC heater supply.

The alternative with a zenerdiode and power transistor will work well until a minimum charge elco voltage of 7 Volts. In this case the transistor should be capable of supplying a high peak current. When the heaters are cold, they have a very low resistance value and are basically a short circuit until they heat up.

When considering DC heater supply think of connecting the heaters in series in stead of parallel. Most tubs used for preamps need a 6.3 V / 300 mA heater supply or 12.6 V / 150 mA. With a few components one can make a regulator capable of supplying 300 mA or 150 mA. Making a regulator for a higher voltage such currents is easier than one for 6.3 V and a higher current.

Have fun developping.

Passenger.

Dirk:
Hallo Passanger,

I do not agree in all parts: most modern 78XX - in this case / example the 7806 - will work fine with 8 V after the first cap. I have had no problems yet with 7806 and Hammond transformers but I consider that there are also transformers available which a rated wrong  and if one uses such a transformer one might run into problems.
Of course there is no need for DC heating if the layout of the amp is OK and normaly 6,3 V AC will do a good job but as I wrote already if the amp is in a very small housing it will be worth to think about DC heating BUT I must stress this won't be an overall solution because you can step into other pitfalls caused by the transformer itself e.g. if it is placed to closed to the signal itself....

Best regards, Dirk

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