Tubes Valves Toobs

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ecs113

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Can anyone recommend a 12a*7 type tube with poor high frequency response?
 
Sorry to burst your bubble, but ANY tube will have a bandwidth significantly greater than the full spectrum audio bandwidth. You can limit the frequency with capacitors, or you can get some fuzz by overdriving it, but the natural bandwidth of even the cheapest types are well above the audio band.
 
Mullards are known to have a darker sound than most other 12AX7's/ECC83's.

12AY7's & 12AU7's are lower gain dual triodes and tend to have more mids.
 
haburton said:
Sorry to burst your bubble, but ANY tube will have a bandwidth significantly greater than the full spectrum audio bandwidth. You can limit the frequency with capacitors, or you can get some fuzz by overdriving it, but the natural bandwidth of even the cheapest types are well above the audio band.
Click to expand...

Bubble? It was a simple question...
 
M.Brane said:
Mullards are known to have a darker sound than most other 12AX7's/ECC83's.

12AY7's & 12AU7's are lower gain dual triodes and tend to have more mids.
Click to expand...

Ok, here's the problem:
I am using Yellowjackets w/ JJ EL84's in the power section of an amp used to seeing 6L6's. (I am using a 12AY7EH and a Sovtek 5751 in the preamp section and a 12AT7EH for the phase inverter.) I enjoy the playability of the Yellowjackets, other than the fact that the high frequencies are out of control even with the treble and presence turned down.

I would get Mullards, but they are quite expensive.
 
Internal resistance and gate capacitance

It's quite a sensible question, really.

Even though any tube - as mentioned - will be able to work at bandwidths far exceeding the audio range, some of them have a number of interface shortcomings.

This has to do with their plate resistance combined with their gate capicitance.

A 12AY7 would - just because of it's low internal resistance - drive more high-frequency into a given (next stage) gate capacitance than e.g a 12AX7. But the gain will be different also!

I would rate the 12XX7 like this - from low to high internal resistance, and hence from bright to dark in a given circuit:

12BH7 - 12AU7 - 12AY7 - 12AT7 - 12AX7

Note that the BH has different pin layout..

So if you're using a 12AY7 now, you should be able to get "darker" results - but higher gain - from a 12AX7...

Hope this makes sense..

Jakob Erland
Gyraf Audio
 
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