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PostPosted: Tue Nov 20, 2012 3:28 pm 
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The issue described in the post below pertains to an earlier version of the Tweed Royal kit documentation and has since been corrected. The corrected hi-def wiring diagram is available for download at http://www.buildyourownclone.com/tr_wiring. Please download this new version and delete any older copies.

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Due to an error in the Tweed Royal wiring diagram, the amp's "Cut" control pot will not work properly. This control is designed to add negative feedback to the signal at the second preamp tube as it's turned up, reducing gain and increasing clarity. At the full CW setting, it is designed to add the same amount of negative feedback that the 5F1 Tweed Champ circuit has hard-wired into it. So if you want to run the Tweed Royal in "full Champ mode", you'd select the S.E. (single-ended) operating mode on the rotary switch, dial the Cut control all the way up, and leave the Tone control all the way off (bypassed).

Unfortunately, due to the wiring diagram error, which switches the connections between the two sides of the V2B cathodyne phase inverter and the grid pins of the two 6V6 output tubes, the phase of the feedback signal is reversed, and the Cut pot becomes a positive feedback control. This has the opposite effect of the one intended, and will likely cause the amp to oscillate (i.e. squeal) at higher settings of the cut control. And since the oscillation originates after the volume control, it will squeal at full amp volume. I've heard it, and believe me, it's not an attractive sound, though it would make a good home security system alarm signal. If you own a cat or dog, it will never forgive you.

The fix is an easy one, however. Just switch the two leads connected to the #6 pin on each 6V6 tube socket versus what is shown in the TR wiring diagram. In other words, the purple wire in the diagram should go to the #6 pin of the right-hand output tube socket, and the brown wire should connect to the #6 pin of the left-hand output tube socket. If you have already wired the amp and are correcting this mistake, you will likely need to splice an extension to the purple wire in the diagram in order to reach the right-hand socket. If you do this, be sure to insulate the splice (heatshrink, electrical tape, etc.) so that no wire is left exposed.

UPDATE: I have done this fix on my own Tweed Royal, and it is now VERIFIED effective (as I was sure it would be). The cat just came out from under the bed....

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PostPosted: Tue Nov 20, 2012 7:09 pm 
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You can also swap the OT primary wires.

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PostPosted: Tue Nov 20, 2012 7:33 pm 
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True. Just figured it was easier to switch two than four.

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PostPosted: Tue Nov 20, 2012 7:54 pm 
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duhvoodooman wrote:
If you own a cat or dog, it will never forgive you.
UPDATE: I have done this fix on my own Tweed Royal, and it is now VERIFIED effective (as I was sure it would be). The cat just came out from under the bed....

:lol: :lol: :lol:

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PostPosted: Tue Nov 20, 2012 8:04 pm 
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duhvoodooman wrote:
True. Just figured it was easier to switch two than four.

Only two I think

The PP Tweed Deluxe transformer doesn't use NFB I think (at least the real one doesn't).

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PostPosted: Tue Nov 20, 2012 8:47 pm 
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ChrisM wrote:
duhvoodooman wrote:
True. Just figured it was easier to switch two than four.

Only two I think

The PP Tweed Deluxe transformer doesn't use NFB I think (at least the real one doesn't).

This one does. Keith installed a 22K resistor in series with a 250K pot with an integrated DPDT switch between the V2A cathode and the output jack tip. With the switch off, a 25uf cap is added between the cathode and ground. With it on, this "Cut" control adds negative feedback through 272K of resistance at the initial turn on position, decreasing to 22K (the 5F1 NFB resistor value) at the full CW setting. So you can run at the 5F1 NFB setting with the SE rotary switch setting and with the Tone control bypassed for "Tweed Champ mode", and with the NFB switched off and the Tone control engaged with the PP switch setting for "Tweed Deluxe mode". And a whole bunch of other stuff in between. Quite the flexible little amp! Especially now that it doesn't set off the glass breaker detector on my home alarm system.... ;)

Here's the schematic link, if you'd like to check it out, Chris: http://www.buildyourownclone.com/tr_schematic

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