A while back I bought a Kitty Hawk M1 amp.
However, I soon saw that this implementation deviated from the schematic that is circulating on the internet:
http://www.kittyhawkamps.com/schaltplaene/m1preamp.jpghttp://www.kittyhawkamps.com/schaltplaene/m1_m3_endstufe.jpg
What immediately strikes me is the combination of EL34 and 6L6 power tubes.
In addition, I did not have the switch to switch between EL34 and 6L6 and the Class A / AB switch on the front was also missing.
In short, time for reverse engineering.
This does deviate from the M1 schematics that is circulating on the internet.
There also appears to be a tda2030 for the reverb.
The main thing that stands out is the power amplifier.
There seems to be a gain stage after the phase shifter. Has anyone seen this before?
As mentioned before, there are 2 types of power tubes in the power amplifier. Namely a pair of EL34 and a pair of 6L6.
Now these all have the same bias voltage and anode voltage. This doesn't seem right to me.
Then measurements were made on the power tubes. Below the result.
V7 - EL34
V8 - EL34
V9 - 6L6
V10 - 6L6
V7:
60W 81mA
120W 67mA
V8:
120W 68mA
Q9:
120W 52mA
V10:
60W 74mA
120W 67mA
Measurement on tube V9 deviates a lot from the rest.
Switched V9 and V10 for the test and did another test on the position of V10.
V10:
60W 60mA
120W 50mA
Doesn't seem like this tube is completely within spec?
And the rest of the currents, aren't they set very high?
For example, if I enter the data for an EL34 on this site: http://mail.robrobinette.com/Tube_Bias_Calculator.htm I could get about 38.9mA at 70% disipation.
This makes a significant difference.
In addition, the settings for both EL34 and 6L6 appear to be equal with the same bias voltage. This isn't quite right either, is it?
However, I soon saw that this implementation deviated from the schematic that is circulating on the internet:
http://www.kittyhawkamps.com/schaltplaene/m1preamp.jpghttp://www.kittyhawkamps.com/schaltplaene/m1_m3_endstufe.jpg
What immediately strikes me is the combination of EL34 and 6L6 power tubes.
In addition, I did not have the switch to switch between EL34 and 6L6 and the Class A / AB switch on the front was also missing.
In short, time for reverse engineering.
This does deviate from the M1 schematics that is circulating on the internet.
There also appears to be a tda2030 for the reverb.
The main thing that stands out is the power amplifier.
There seems to be a gain stage after the phase shifter. Has anyone seen this before?
As mentioned before, there are 2 types of power tubes in the power amplifier. Namely a pair of EL34 and a pair of 6L6.
Now these all have the same bias voltage and anode voltage. This doesn't seem right to me.
Then measurements were made on the power tubes. Below the result.
V7 - EL34
V8 - EL34
V9 - 6L6
V10 - 6L6
V7:
60W 81mA
120W 67mA
V8:
120W 68mA
Q9:
120W 52mA
V10:
60W 74mA
120W 67mA
Measurement on tube V9 deviates a lot from the rest.
Switched V9 and V10 for the test and did another test on the position of V10.
V10:
60W 60mA
120W 50mA
Doesn't seem like this tube is completely within spec?
And the rest of the currents, aren't they set very high?
For example, if I enter the data for an EL34 on this site: http://mail.robrobinette.com/Tube_Bias_Calculator.htm I could get about 38.9mA at 70% disipation.
This makes a significant difference.
In addition, the settings for both EL34 and 6L6 appear to be equal with the same bias voltage. This isn't quite right either, is it?
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