Members mcr23 Posted January 20, 2010 Members Share Posted January 20, 2010 OK so someone explain the difference between amps with chokes and amps that use caps instead? (inpsires from the ENGL thread) Also, I know I've asked in the past but what is different about cathode-foller preamp positions? Why do they have a cathode follower in the first place, while other amps or preamp positions in the same amp do not? Finally, if the same power toob responds differently in individual circuits, what are some general guidelines as to why this is so? Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted January 20, 2010 Members Share Posted January 20, 2010 Finally, if the same power toob responds differently in individual circuits, what are some general guidelines as to why this is so? Power tubes respond differently in different circuits because there are a lot of different variables in a power section that affect the tone and output wattage, such as: Amplification class (A vs. A/B), supply voltage, OT Primary impedance, bias supply design, plate resistor value, etc... All of these things will affect how "clean" the power section is and how the specific tubes will react in the amp. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 Cathode followers are unity-gain stages, I.E. the signal size coming out of the tube is the same as the signal going in. They are used to match the impedance between sections of an amp (like in front of the tone stack in Marshalls) and to match the output impedance in FX loops. VHT amps use CF after the phase splitter to drive the power tubes. It's also a tonal choice - the 5150 doesn't have a CF to drive the tone stack, and it has a pretty significant affect on the tone. Once again, it's totally up to preference. Thanks! So, regarding the phase splitter.... do you think different 12AX7s would drive the power section differently? I remember Doug mentioned NOT to use the New Sensor tubes in cathode-follower stages ebcause he said they don't hold up well. Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted January 20, 2010 Members Share Posted January 20, 2010 I remember Doug mentioned NOT to use the New Sensor tubes in cathode-follower stages ebcause he said they don't hold up well. That's true. The CF stage sees a LOT more voltage than the other stages (like double), so you'll need a robust tube. The important thing is to make sure that the tube in question DOES NOT have a spiral-wound filament. Those can't handle the higher voltages of CF positions. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 Link to comment Share on other sites More sharing options...
Members newholland Posted January 20, 2010 Members Share Posted January 20, 2010 oh man.. you can totally transform an amp with a different phase inverter. my mesas ALWAYS sounded thoroughly different with a fresh one-- but when i tried an AT.. it really changed the amp utterly. different feel, less squishy-compressy, and felt a lot more fendery, actually. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 I should try putting some of my NOS tubes in the PI slot to see how they do. Grey plates, black plates, etc. Link to comment Share on other sites More sharing options...
Members Zozobra Posted January 20, 2010 Members Share Posted January 20, 2010 Good article on cathode followers:http://www.freewebs.com/valvewizard/accf.html A small mention on chokes/screen grid supplies:http://www.freewebs.com/valvewizard1/smoothing.html Link to comment Share on other sites More sharing options...
Members Sixtonoize Posted January 20, 2010 Members Share Posted January 20, 2010 Very cool links.Kinda techy, but killer info. Link to comment Share on other sites More sharing options...
Members t1r2u3s4t Posted January 20, 2010 Members Share Posted January 20, 2010 http://www.aikenamps.com/Chokes.html Link to comment Share on other sites More sharing options...
Members SG-DAWG Posted January 20, 2010 Members Share Posted January 20, 2010 I dont like your tone of voice. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 Nice Link to comment Share on other sites More sharing options...
Members NinjaRaf Posted January 20, 2010 Members Share Posted January 20, 2010 So a choke will make an amp tighter? How hard are these to install? Link to comment Share on other sites More sharing options...
Members eyeball987 Posted January 20, 2010 Members Share Posted January 20, 2010 I use 5751's in the PI spot of my Randall RM's and notice a decent increase in clarity. Also seems to smooth them out a touch. I just ordered two more today actually. Link to comment Share on other sites More sharing options...
Members the_bleeding Posted January 20, 2010 Members Share Posted January 20, 2010 So a choke will make an amp tighter? How hard are these to install? Not hard. You just need mounting space on your chassis somewhere. But other than that, you just pretend its a resistor with very long wires. Put it after your first filter cap, in series with the power supply. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 this gave me some good reading. As did other things on the Aiken website Link to comment Share on other sites More sharing options...
Members kayman121 Posted January 20, 2010 Members Share Posted January 20, 2010 I should try putting some of my NOS tubes in the PI slot to see how they do.Grey plates, black plates, etc. Tube type will make the biggest difference in PI, specifically the transconductence of the tube. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 Maybe I'll score some 5751s then Link to comment Share on other sites More sharing options...
Members Badside Posted January 20, 2010 Members Share Posted January 20, 2010 That's true. The CF stage sees a LOT more voltage than the other stages (like double), so you'll need a robust tube. The important thing is to make sure that the tube in question DOES NOT have a spiral-wound filament. Those can't handle the higher voltages of CF positions. It's not the voltage so much as it is the cathode-to-heater voltage.See, the cathode-follower is sort of biased the other way around (with a 100K resistor on the cathode instead of the anode/plate). So instead of having the cathode at say 2V, it's floating at something like 120-150V depend on the amp. Being close to the filament, it starts drawing electrons from the filament at a much faster rate. Basically, different tubes have different cathode-to-heater voltage handling. I think it's important to mention also that a 12AX7 basically makes a really bad cathode-follower, and this is precisely why we love it! It will compress one side of the signal wave more than the other, warming up the sound a bit (strong on 2nd order harmonics). It's an important part of the Bassman/Marshall circuit. Link to comment Share on other sites More sharing options...
Members Badside Posted January 20, 2010 Members Share Posted January 20, 2010 Tube type will make the biggest difference in PI, specifically the transconductence of the tube. This is so true!!! I remember how I couldn't believe how good my DSL50 sounded in comparison to other DSLs I had heard. Even soundmen commented on that. Then, when I retubed it last year (it's now my bandmate's amp), I realized all that time I had a 12AT7 in the PI slot. I had completely forgotten about it!Putting a regular ECC83 (AX) in there turned it into a mushy bassy mess. So for fun I tried a 12AU7, the amp was now uber clear but a bit thin. Somehow, the AT seemed to be the most balanced. Nice sparkly high-end and balanced low-end. Note that metal heads might still prefer the 12AX7 as it seems to give a bigger low-end.On THAT particular amp that is... Impressive stuff! Link to comment Share on other sites More sharing options...
Members Badside Posted January 20, 2010 Members Share Posted January 20, 2010 So a choke will make an amp tighter? How hard are these to install? It also drops less voltage than a resistor and thus may change the sound of the whole amp.The choke usually goes just before the screen supply.My 2204 clone has 487V on the plates and something like 475V on the screens thanks to a big mighty choke. Don't try 6L6s in there!It's also the loudest 2XEL34 I've ever heard. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 MOAR information. Gives it to me. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 Thanks, Rocca Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 rocca, I find your HG30 intriguing. you ever going to get a HG head into the15W range perhaps? Lately I've had low-wattage 6V6 gas. Link to comment Share on other sites More sharing options...
Members mcr23 Posted January 20, 2010 Author Members Share Posted January 20, 2010 cool. I'll have to make sure to PM you when I switch back to govie in Feb/Mar Link to comment Share on other sites More sharing options...
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