Automatic optimize bias control module for four triode output stages or four pentode push-pull (PP) amplifiers, 100 x 57 mm.
|Price :||58,00 €|
This module has been designed to maintain a constant bias voltage through all power output tubes for your tube stereo power amp.
The bias is kept at a constant level on the output tubes, irrespective of the signal level.
The advantage of using the ABF-Q module is that it will extend output tube life, in a lot of cases it will also improve the sound and last but not least, you will never have to worry about adjusting the bias again.
The ABF-Q module has four blue LED’s, one for each output tube, which when lit, indicate that bias is at the correct level and that all is good with each tube.
Should any of these blue LED’s go out or not go on after power up, means that here is an issue with that given output tube and that the tube in question needs to be immediately replaced.
When the amp is powered up, at first a red LED will be on, indicating that there is power to the ABF-Q module. The red LED will go out after about 20s.
After a further delay of between 40-50s, each of the blue LED’s should come on indicating that the bias is now set and stable for each output tube. The amp is now ready to use.
The ABF-Q is suitable for class A, AB and C tube amplifies.
Presetting the ABF-Q module bias level:
Before the ABF-Q module can be wired up, you need to preset its bias voltage.
As an example, for EL34 tubes, we recommend a bias voltage of 425mA, for KT88 tubes we recommend 450mV. You will need to consult the tube specifications in order to determine the optimal bias voltage for the tube in your amp.
This bias level is set using the blue colored trimmer on the ABF-Q module.
We strongly recommend that you preset the ABF-Q module before you proceed with installing it into your tube amp!
The ABF-Q has an isolation transformer for the 230VAC supply, so simply connect your amps 6.3VAC filament supply to the two terminals under the transformer.
Place your ABF-Q module on a non-conductive surface. Apply power to the ABF-Q module and you should see the red LED on the ABF-Q module light up. This LED will go out after about 20s.
Set your meter to read DC and to the lowest scale, say 1V, 2V or 5V. Put the black meter lead on any GND pad on the ABF-Q module and put the red meter lead on the pad next to electrolytic capacitor, see below. Now adjust the blue trimmer until the desired bias level is achieved.
That’s it, you just set the ABF-Q module to the desired bias operating level.
PP stage 2 x EL34, class AB1, ultra linear:
To set the bias for an EL34 tube, the recommended anode current for AB1 class is 42.5 mA. We therefore set the bias at 425 mV (0.425 V).
Unplug the power cord, wait for half a minute or so and disconnect the wires from the mains terminals on the ABF-Q module.
DO NOT EVER readjust the trimmer once the ABF-Q module is installed and wired up. The whole idea is to set in ONCE and forget!
Installing and wiring the ABF-Q module into your tube amp:
Please refer to the drawing below, which shows a typical tube amps connection for your ABF-Q module.
The HiV input is only connected if the amplifier is equipped with a delayed connection anode voltage and connection with a time of more than 20 seconds.
In this case the jumper S2 must be disconnected (remove jumper see fig.) !
Use this diagram as a reference to the wiring of the ABF-Q module into your amp. Only one channel is shown, the other channel is identical.
This now pretty much completes the wiring of the ABF-Q module into your tube amp.
Double check all the wiring steps again, even triple check them
Once you are confident that all your wiring is correct and as per the above steps, it is time to test your ABF-Q module installation.
Plug in all tubes, that is the driver tubes, power tubes and the tube rectifier. In order to see the blue LED’s on the ABF-Q module, place your amp on its side.
Maybe stick a piece of styrofoam under one of the output transformers to cradle the amp chassis so that the tubes do not touch the bench top.
Connect an 8 or 4 OHM dummy load or your speaker.
Power up your amp. The red LED on the ABF-Q module should come on straight away and will go out after about 20s.
After an additional 40 to 50s, each of the blue LED’s on the ABF-Q module should start to come on, which indicates that each output tube has reached the preset bias level and all is good. Excellent!
You can measure the actual bias voltage on each output tube with a meter just to double check.
Set your volt meter to the 1V, 2V or 5V scale in DC volts. Put the red meter lead on the cathode pin of the tube socket and place the black meter to the chassis star ground tag. The meter should read close to your preset bias voltage. This reading might be a little higher to start with and will get close to or exactly to the preset bias voltage as the output tubes warm up.
Do this measurement for each output tube.
Leave the amp running for about 10 minutes, all four of the blue LED’s should remain lit.
Power down the amp and let everything cool down a bit. Remove dummy load, if that’s what you used, or disconnect your speaker.
Re assemble your amp and place it in its spot.
Power up your amp and after about 60s or so, the amp is ready!
If things do not work as they are supposed to:
If the red LED on the ABF-Q module does not come on immediately after the amp is powered up, power it back down and check the 230VAC wiring to the ABF-Q module.
If none of the blue LED’s come on after the 40-50s soft start delay, power the amp back down. Check all your wiring from the ABF-Q module to your amp.
If say only three or two of the blue LED’s come on after the soft start delay, power the amp back down and check the wiring to that particular tube for which the blue LED did not go on for. Also check to make sure that the pins in that tube socket are nice and tight and that the tube fits into the socket not at all loose. Also check the pins in the tube socket of any oxidization, if they are dirty, perhaps use Deoxit or similar to clean the pins!
Do’s and don’ts:
Do check that the pins in each tube socket are tight and that each tube does not fit loosely in the socket.
Do check that the pins in each tube socket are clean of oxidization, use Deoxit or similar if they are not clean.
Good fitting and clean pins in tube sockets make ALL the difference!!
Don’t do a lot of tube rolling! This is a sure way to loosen up the pins in your sockets! If you cannot help yourself and you must do tube rolling, check the tightness of the pins each time you swap tubes!
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