Re: [Harp-L] technical help

["Bob Blunn" <bblunn@xxxxxxx>]

Hi Mike,

This type of tube swap will require more than a single resistor change.  While the 7F7 and 6SN7 are both dual triode tubes they are not pin compatible.  (I checked the specs via http://tdsl.duncanamps.com/tubesearch.php<http://tdsl.duncanamps.com/tubesearch.php>)  Hopefully you haven't yet done the swap and powered up the amp.   It may not pass the smoke test.

Since tube amps contain lethal voltages (EVEN WHEN UNPLUGGED) it is usually recommended to leave these types of mods to an amp tech.  Many musicians also work on their own equipment, (I'm guilty as charged!), but I'm also an electronics engineer and kinda know what I'm doing. At least enough not to get killed.

If you want to adjust the gain of the preamp section of your amp that can be done by changing some component values.  (Usually a capacitor/resistor pair.)  If you are comfortable with tearing into your amp, ripping it's guts out, and replacing them in your quest for tone, then there are plenty of resources online to help you out!   Here's a good starting point...

http://www.diycustomamps.com/diyamplinks.htm<http://www.diycustomamps.com/diyamplinks.htm>

Knowing more about what you have, and what you need to do, would help get a better answer.  What type of amp is it? What year/make/model?  Is this for harp?  Guitar? Other?  Do you desire - More distortion/breakup at lower or higher volumes?

Best Regards,

Bob Blunn



--- In harp-l-archives@xxxxxxxxxxxxxxx<mailto:harp-l-archives@xxxxxxxxxxxxxxx>, mike reid <shrimpdaddymike@...> wrote:
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> i've just swapped a 7F7 pre amp for a 6SN7 because of the gain difference i need to adjust the value on the resistor would anyone know what value i should adjust this to?
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