martin manning wrote: ↑Sun Jul 21, 2019 12:04 pm
Fred, do you have an updated schematic for this amp? Skimming through the thread I don't see one that shows the Tweed section and the mixing.
Hey Martin, thanks for jumping back in the conversion.
I wish I had seen your answer earlier, sorry about that.
You are right, I have not updated the schematic. I will do so today, and post it here.
I have ordered a 12AU7 and a 12AY7. I am curious to see how the Tweedle Dee channel sounds with these!
martin manning wrote: ↑Sun Jul 21, 2019 12:04 pm
Fred, do you have an updated schematic for this amp? Skimming through the thread I don't see one that shows the Tweed section and the mixing.
For some reason I missed a part of the conversation, as my mobile app does not work anymore. I did not get any notification of your messages and want to apologize for not following up with you guys.
There is the updated schematics. I hope I did not make mistakes.
It represent the state of the amp now : 2 x 220k resistors in series at the output of the TD and 220k on the BM output.
I received the tubes yesterday and tried the 12AY7 this morning as suggested by Tony.
It brought the distortion of the Tweed Channel down and starts to crunch around 6.5 when I dig in the strings hard.
When measuring the output signal, it goes up a lot more slowly but eventually goes higher than with the 12AX7.
I mesured more than 80v on the output when everything is on ten for the TD channel.
I now have to try and remove the mixer resistor. I still have 220k + 220k on the TD channel and 220k on the bluesmaster channel.
I hesitate as it sounds pretty glorious so far.
I will try and record something today.
Thanks again for the help and suggestions, I really appreciate it !
Thanks Fred, the up-to-date schematic makes it much easier to understand what you are doing. Seems like the Tweed channel needs some attenuation before mixing, and I wonder about hitting the CF loop driver stage with the full output from the preamp. You might consider a divider in front of that the drop the input to that stage down to line level or slightly above.
With the 12AY7, the channel has now more headroom and easier to work with. I really love the sort of raw m tone that seems to cut through whenever I switch from the bluesmaster channel.
I feel like I will need to keep the voltage divider as long as I don't have the relay to switch to ground the unused signal, because the two channels are bleeding into one another. Plus the amp would oscillate when I would try to shut the pots of the unused channel. Adding 220k mixer resistors helped in the way that it reduced the output level and stopped the oscillation.
Bringing the signal down to line level (0.3 to 2 V) could be an option, but how much resistance should I add? I think I would probably be better of with Marcus and Erwin's suggestion of using a pot as a variable resistor after the coupling cap of the TD channel.But then with the added resistor value, how would it affect the tone of the bluesmaster channel?
Thanks again for your time and knowledgeable advices!
Fellow members, I finally found time to redo the input relay. I now have the input jack feeding both Tweedle Dee and Bluesmaster preamps, and I rewired (actually redo from scratch) the relay board. I added a 250k piher pot after the DC coupling cap on the output of the Tweedle Dee channel and before entering the relay, with the excess signal being grounded. I suppose the pot act as a voltage divider, but I am assuming it keeps the original flavor of the output signal, while taming the strength of the signal. I kept the Bluesmaster output as is, no more resistor on the output after the DC cap.
Results:
Switching from Tweedle Dee to the Bluesmaster is totally silent, a real improvement. No more pop.
Bluesmaster channel is a bit stronger (full signal flowing from the preamp stage into the D-lator) and seems to be bassier than before.
I left the piher pot in the original position and did not play with it yet, so it is basically allowing 50% of the signal through (correct me if I am wrong here). It seems to still be too much for the D-lator, because when I add it to the chain (I can bypass D-lator and feed the MV directly with the flip of a switch) with input pot , drive pot pot and output pot at noon with no effects in, it adds a saturation that sound like a resistor saturation not tube distortion, it sounds muddy and Mid focused..
I will try to ground more of the output signal at the piher pot and report.
I have been doing some mileage on the cab in the meantime, and should apply the Tweed covering this weekend, will post pictures as soon as it is done.
Thanks again for all the help and support, I feel the end is very near !
I switched the 12AY7 for the 12AX7 (more gain out of the Tweedle Dee channel!
Love this amp so far with 6L6GC, still have to try it with EL34. I will try and make a recording with both tube types so I can compare which one I prefer.
Been putting three coats of shellac on the cab and I like the color so far. Stille have to attach the handle, bought some bolts, but these are a little too long..
It couldn't have been possible without the help of all you guys, so thanks again for the help and all the suggestions!
Cheers!
Fred.
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Last edited by fred.violleau on Mon Oct 28, 2019 9:33 pm, edited 1 time in total.
I must say Tweed is a bit more challenging than regular tolex.
I will try and record some sample this weekend with a proper setup. I did some recordings with my phone last weekend, but it keeps on compressing the sound way too much.
On a side note I think my Thiele cab sounds like sh#$t and I am wondering if it is related to a toasted speaker. The EVM12L in it has nothing but a few ink stamps on it, probably dating from the late 80s. I bought it used cause I had one back in the late 90s with a Mesa black Shadow 200w and that cab was killing it: clarity, bass response, depth and warmth... This one is just responding to mid and treble frequencies. As a comparison, I have 2 x12 cab loaded with WGS ET12 90 that is killing it, lots of bottom and overall great sound.
Great looking amp Fred. I really like the tweed look and the lighter color grill cloth !
Excited to here clicks. Definitely sounds like a new speaker is needed. A WGS12L might be a good option but they are hard to get here in Canada.
