Tweedle Dee / mods or not?

[sluckey]

The input and output are marked on the terminal strip. Ampeg Gemini II used a .1µF at the input. You may not need an output cap, depending in the circuit that follows. Look at this...

http://sluckeyamps.com/phoenix/phoenix.pdf

[ChopSauce]

EDIT: I've been mistaking, sorry. This tone stack seems to require a coupling cap before it.

If you intend to replace the deluxe tone stack with this one, the input should be the coupling cap before it (cap connected between V1/pin1 and the 100k plate resistor). The output should go to the wiper of the corresponding volume pot. At least, that's how I understand the schematic.

But keep in mind the tone stack will be significantly lossy compared to the tweed tone control. You will be hitting grid of the next stage with less signal. This is a big change...

[ChopSauce]

So, upon Fred's suggestion, I am tempted to buy the inMADout (most likely) https://www.tube-town.net/ttstore/tt-po ... e-5e3.html power transformer, which pulls out 150mA on the HT for much cheaper (67€) than the Hammond AEX, but still I could read that the "agonizing" power transformer was part of the Tweed Deluxe sound, so...

I'm tempted though to strip this an build a 5E5 ...

I have been also, especially as Tube Town sells this https://www.tube-town.net/ttstore/tt-po ... power.html even beefier power transformer (from inMADout also, probably) for 79€, but then, that raises the question of the OT...

... put a trimmer instead of the 680k on the cascading relay so you may play with it ! I would ground the excess signal...

I made a schematic for the (stock Tweedle Dee) circuit when the inputs are cascaded.

cascadedInputs.jpg

Note that the signal is already grounded through the 1M grid leak resistor of the bright input.

EDIT: if you add a resistor R_ig to ground to the 680k inline resistor, then R_ig will appear parallel to the 1M resistor at the bright input (V1A grid leak). So using a 1M value for R_ig, you'll cut in half the grid leak value, in third using a 500k resistor, etc. The same maths applying to a pot as well.
Now, it could be interesting to compare these values with typical OD entrance ones.

[fred.violleau]

Interesting ! So you may not ground the excess signal then, you would end up having a variable resistor isn't it?

What's the status on your build BTW?

Fred.

[ChopSauce]

Actually, I didn't thought about it but it is a possibility, yes. Good point.

So far my build pauses at the board being populated with just a Dumble/hi-plate "voiced" raw (normal) channel - as per Marcus' (& your?) suggestions - departing from the original Tweedle Dee.

DSC_5987.jpg

I'm currently missing time to build a repro 5C3 chassis with an additional pot for a VVR / power scaling as a second mod. So far, I don't feel like I'll go much further with mods.

[fred.violleau]

I am still trying to find the best solution for the master volume pot.
So far I have tried the following:
- pre phase inversion. Didn't like it as it was altering the sound too much
-Lar Mar Post Phase inversion. Would not alter the sound which I really enjoy. Tried 1MA pot and 1MB as I though the linear pot would allow a complete control over the full course of the pot compared to the log one.

Unfortunately the 1MB has a very limited course: volume start from 0 to full volume at 1/3 of the course and nothing else on the remaining run of the pot.

Anyone knows why? Is it because of the cathodyne?

Should I try a lower value so it would distribute the action over the full course if the pot? But then would it affect the sound as well ?

What's your take on this one?

Fred.

[martin manning]

For the Post-PI (Lar-Mar) I would follow the recommended path of replacing the 220k grid leak resistors with a 250kA (log taper) dual pot, feed the 1k5 grid stoppers from the wipers, and connect 2M2's to ground for protection against the wipers losing contact.

[fred.violleau]

Hey Martin, thanks for jumping in!
So you would recommend something like this implementation :

PPIMV_JTM45.png

Oh lordy lord, got to order online again...

Thanks a lot for sharing, again

Fred

[martin manning]

So you would recommend something like this implementation :

Yes, electrically it would be just like that, except the shield is grounded instead of going to the negative bias voltage.

[norburybrook]

and remember folks that's a 10M NOT a 1M at the node with the 3.3M on the P.I.

it made a nice subtle different to me when I swapped that.



M

[fred.violleau]

Lol Marcus, I have made so many mistakes as well, that I find these old amps are very forgiving

Thanks again Martin for that nuance! So If I were to add a fixed bias on this build I would have to switch the ground in order to connect it to the bias current board, right?

Fred.

[norburybrook]

Lol Marcus, I have made so many mistakes as well, that I find these old amps are very forgiving

Thanks again Martin for that nuance! So If I were to add a fixed bias on this build I would have to switch the ground in order to connect it to the bias current board, right?

Fred.

Fred,

Did you miss Charlie Wilsons posts? this was labelled as a 1M on the schematic and layout we all used to build our amps. Last week Charlie was revisiting his photos of the original amp and realised that he'd make a mistake , he'd seen the band as green rather than blue, so this is a new change.




M

[martin manning]

So If I were to add a fixed bias on this build I would have to switch the ground in order to connect it to the bias current board, right?

Either way the MV wiring would be the same, with the shield connecting to what was the junction of the two 220k resistors, but for fixed bias that junction would then connect to the negative bias (like in the JTM45 drawing above) instead of ground (like the cathode biased Tweedle).

[fred.violleau]

Fred,

Did you miss Charlie Wilsons posts? this was labelled as a 1M on the schematic and layout we all used to build our amps. Last week Charlie was revisiting his photos of the original amp and realised that he'd make a mistake , he'd seen the band as green rather than blue, so this is a new change.




M

@Marcus, holly guacamoly, I did miss that post! I though you were joking about a mistake you made. I will make the change on mine too. I suppose you did, so what does it brings to the amp?

Martin, thanks again, everything is crystal clear!

Fred.

[norburybrook]

Fred,

Did you miss Charlie Wilsons posts? this was labelled as a 1M on the schematic and layout we all used to build our amps. Last week Charlie was revisiting his photos of the original amp and realised that he'd make a mistake , he'd seen the band as green rather than blue, so this is a new change.




M

@Marcus, holly guacamoly, I did miss that post! I though you were joking about a mistake you made. I will make the change on mine too. I suppose you did, so what does it brings to the amp?

Martin

I htought so

personally speaking I felt it made the gain smoother in tone and also the onset of gain seemed smoother......so I think the word is ...'smoother' ....


It's subtle but on my amp I felt it made a worthwhile change.

YMMV with these things though.


M