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Orange AD200B Mk II Bass Amp

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  • doombass
    replied
    It's been a busy weekend so kind of late posting, sorry. The resolution of these original schematics are really lousy to say the least, but they're all I've got:



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  • ratlordfx
    replied
    Nice! Thanks. I am still not seeing a 3.9k resistor in the power supply, but these are the pre and power amp schematics I found, and there are major discrepancies between it and the model i am working on. Let me know if you see one on the original schematic

    Thanks again,
    Jason

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  • doombass
    replied
    Here are the unofficial schematics that used to be located at the non functioning Photobucket-link above:





    I did'nt seem to find R26 and I don't know how accurate the designations are on these schematics. It's a fairly simple construction so you might find your way anyhow. I have the official schematics on my homecomputer (I'm at work now) if needed.

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  • ratlordfx
    replied
    Does anybody still have a working link for schematics on the MkIII? I have one with KT88's installed, and R26 looks like it got crispy hot. It's color coded as a 3.9k, but measures around 4.2k ohms. Also 2 of the 1K ohms resistors going to the grids seem to have drifted down to around 970 ohms. It came in with lots of noise on the output. Any help is much appreciated 😊

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  • tubesfreak
    replied
    Greetings, Folks! I'm a newbie in the forum, but have been following the thread for some time. Having the same interest in building my own ad 200, with sufficient-tons of info I get here, it's time to join in :grin: Again thanks to bernard!

    I'm planning to replace the power tubes to 3 pairs of EL 36s, as described by Mr. Chambers on his ridicoulously high-powered amps, 12 EL 36s are able to pull 500+ watts of power, so I figured 6 of them would do half of it, which is more than I need..

    Cheers..
    Last edited by tubesfreak; 04-08-2012, 06:21 PM.

    Leave a comment:


  • Flipos
    replied
    Hey guys, from the schematics provided by Bernardduur would it be possible to build the ad200b mk3??

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  • Bernardduur
    replied
    Originally posted by spy View Post
    Bernardduur, thanks for the schematics!

    I'm trying to rebias an AD200 Mk3, too. I have read the thread but I didn't understand the part with the fuses...

    I installed a new set of SED 6550 and 4 1Ohm resistors where the PCB says 1Ohm to measure cathode current at each tube. Do I have to take off the fuses or something like that? Or my measurements across the 1Ohm resistors will be correct?
    With the trimmer set fully biased my maximum readings are 20mA per tube! That's Ice Cold as TDS said.

    If I install a 68K resistor in parallel with the stock 68K at the bias circuit will I have the advantage to bias the tubes hotter?
    I wired the fuses completely out of the circuit as they were giving the kathode an unstable current. The fuse resistance varied with temperature and load.

    Now, with the 1 ohms to ground directly I got good readings from the tubes.

    With the 68k parallel I got her to fully functioning and MUCH better sounding!

    Leave a comment:


  • spy
    replied
    Bernardduur, thanks for the schematics!

    I'm trying to rebias an AD200 Mk3, too. I have read the thread but I didn't understand the part with the fuses...

    I installed a new set of SED 6550 and 4 1Ohm resistors where the PCB says 1Ohm to measure cathode current at each tube. Do I have to take off the fuses or something like that? Or my measurements across the 1Ohm resistors will be correct?
    With the trimmer set fully biased my maximum readings are 20mA per tube! That's Ice Cold as TDS said.

    If I install a 68K resistor in parallel with the stock 68K at the bias circuit will I have the advantage to bias the tubes hotter?

    Leave a comment:


  • Bernardduur
    replied
    Originally posted by TDS View Post
    Could you tell me, was the 474 VAC and 267VAC on load? i.e. not on standby.
    Yep; on load!

    Leave a comment:


  • TDS
    replied
    Originally posted by Bernardduur View Post
    As for the MKIII

    1. I'll check back when I biased her correctly!

    2. 474 VAC and 267 VAC

    3. Woops; I'll correct that!

    4. They are 3mm LED's. They'll light when a fuse is down
    Could you tell me, was the 474 VAC and 267VAC on load? i.e. not on standby.

    Leave a comment:


  • Bernardduur
    replied
    Oh, and I 'fixed' the bias by adding another 68k parallel to the onboard 68k.

    Leave a comment:


  • Bernardduur
    replied
    Originally posted by TDS View Post
    I am also a fan of using 1 ohm resistors in the cathode path of the output valves. Safe and simple and accurate measurement, as long as you remember to subtract the screen grid current from the cathode current

    Is it not possible to arrange the tapping point for the 1 ohm resistors so that the measurement is not being made across the fuses as well as the resistors?

    I guess that the reason the bias supply lacks the range you are looking for is possibly because Orange apparently recommend a current range of between 18mA (Cool) and 22mA (Hot) more like Ice Cold and Luke Warm!

    What is the bias voltage range that you are getting at he moment?

    A small side issue, looking at your calculation, is the max dissipation of your 6550's 46 watts? The highest reference I can see for the 6550EH is 42 watts and that is higher than most other 6550's at 35 Watts.

    It should be simple enough to increase the current by pulling down the bias range by adding a resistor in parallel across R46 to give you the adjustment needed. I usually aim for around 50% dissipation, but that is only my preference as a reasonable balance between valve life and tone.
    Datasheet for the 6550 of JJ

    I usually listen per tube amp what suits better....... usually for bass amps I get to 50% - 60%........ 70% for guitar amps!

    Leave a comment:


  • TDS
    replied
    Originally posted by Bernardduur View Post
    I'll answer em later!

    Right now I'm trying to bias the MKIII version. I'm used to most bias versions but as I want my 'clients' to bias em also I usually install the 1 ohm resistors in my builds.

    When I do this in the MKIII the total resistance varies between 2.4 and 4.2 ohm because of the fuses. I decided to leave the fuses out of the circuit and wire the 1 ohm resistors directly to the ground.

    Now when I bias this little amp I can't get higher then 21.2 mA which means approx 13.1W per tube........ My calculations showed that I needed to go to (approx 70% of 46W = 32.2W).

    I hate this little POC


    Guess I need to redesign the bias section. Now when I look back at the stock bias setting (with a set of EHX 6550) the bias was set around 13 mA.........

    Stupid amp
    I am also a fan of using 1 ohm resistors in the cathode path of the output valves. Safe and simple and accurate measurement, as long as you remember to subtract the screen grid current from the cathode current

    Is it not possible to arrange the tapping point for the 1 ohm resistors so that the measurement is not being made across the fuses as well as the resistors?

    I guess that the reason the bias supply lacks the range you are looking for is possibly because Orange apparently recommend a current range of between 18mA (Cool) and 22mA (Hot) more like Ice Cold and Luke Warm!

    What is the bias voltage range that you are getting at he moment?

    A small side issue, looking at your calculation, is the max dissipation of your 6550's 46 watts? The highest reference I can see for the 6550EH is 42 watts and that is higher than most other 6550's at 35 Watts.

    It should be simple enough to increase the current by pulling down the bias range by adding a resistor in parallel across R46 to give you the adjustment needed. I usually aim for around 50% dissipation, but that is only my preference as a reasonable balance between valve life and tone.

    Leave a comment:


  • Bernardduur
    replied
    Originally posted by TDS View Post
    A few questions if it is possible for you to answer:

    MK1 Amp

    1. What are the V4, V3, V2 and V1 voltages.

    2. What are the AC output voltages from the two HT windings to the bridge rectifiers?

    MKIII Amp

    1. What are the V4, V3, V2 and V1 voltages.

    2. What are the AC output voltages from the two HT windings to the bridge rectifiers?

    3. The secondary winding of the OPT shows only one winding for both 4 and 8 ohm speakers. Is this correct?

    4. What type of diodes are D3 and D4 in the poweramp. Is it possible that they are LED's as was used in the Trace Elliot V8 Bass Amp to indicate blown fuses?

    Any answers will be appreciated.
    As for the MKIII

    1. I'll check back when I biased her correctly!

    2. 474 VAC and 267 VAC

    3. Woops; I'll correct that!

    4. They are 3mm LED's. They'll light when a fuse is down

    Leave a comment:


  • Bernardduur
    replied
    I'll answer em later!

    Right now I'm trying to bias the MKIII version. I'm used to most bias versions but as I want my 'clients' to bias em also I usually install the 1 ohm resistors in my builds.

    When I do this in the MKIII the total resistance varies between 2.4 and 4.2 ohm because of the fuses. I decided to leave the fuses out of the circuit and wire the 1 ohm resistors directly to the ground.

    Now when I bias this little amp I can't get higher then 21.2 mA which means approx 13.1W per tube........ My calculations showed that I needed to go to (approx 70% of 46W = 32.2W).

    I hate this little POC


    Guess I need to redesign the bias section. Now when I look back at the stock bias setting (with a set of EHX 6550) the bias was set around 13 mA.........

    Stupid amp

    Leave a comment:

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