Optimize your Drake L-4B or L7 amplifier

To use a triode or more, with grounded grid a BIAS voltage is needed. This is achieved by means of expensive and hard to find high power zener diodes. Tubes such as 3CX1500 / 8877 need expensive power zener diodes, (50W) which are fragile and hard to find. This module is a "transistorized zener diode" It is equipped with a temperature compensated adjustable zener and a Power transistor. It is designed for a maximum operating voltage of 26.5V.

The printed circuit board is of professional quality, made of double-sided epoxy glass, with plated-through holes and tin-plated power tracks.

Supplied assembled, tested and ready to use, only the power transistor is not soldered (3 solders required), so you can adapt its position to suit the amp you're using. Anti-glitch and meters protection are also included.

No other parts are needed, just install and connect the wires and power transistor. Detailed diagrams with parts list, PCB layout, setup procedure and installation diagram are available for download in PDF format.

Remember this circuit it is especially designed for the Drake L-4B and L-7, but can be used on many other amplifiers 

Note: mounting hardware and transistor insulation are provided.

***Important remark***

This module does not use the TIP147 transistor, like those currently on sale on eBay, as it does not offer stable operation.

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Size: 4.8 cm length x 3.5 cm width x 2.5 cm high. 

***Please check the available space in your amp***

Compatible with the following Linear Amplifiers tubes

Tube(s)                     Grid current    Anode current        Bias voltage

3-500Z                     150-200 mA             0.75 A              9 VDC

2x 3-500Z                 350-400 mA             1.5 A                9 VDC

You can adapt it at many others models.......

I ship worldwide

E-MAIL If you have any question, don't hesitate to ask me.

THANKS for your interest on this item!

Note: since part of the price has been transferred to the shipping price in order to minimize the taxes that buyers have to pay, I am unable to offer discounts on grouped shipments.

I Shipping via Priority International Flat Rate Envelope, in order to provide a delivery time, not too long.

I sent no later than 5 working days after payment.

***France is not the next door***

Transit time can be up to 4 weeks, (!! Be patient!!).

I do the maximum in terms of product quality, shipping, and packaging, for everyone to be happy.

***I aspire to have 100% positive feedback***

So I would advise to "impatient people" do not buy if you do not agree with these simple principles,

!!! Remember purchase is not compulsory!!!

Thank you *** to take into account these observations ****

And most importantly, thank you very much for almost 4000 buyers were satisfied.