Hello all. This is a tube guitar amp I designed. I used some transformers recovered from old equipment and would like to get some thoughts and opinions on the design before I start soldering. One place where I just kinda made some educated guesses was with the grid resistors on the EL84. This is my first diy amp, so any help would be greatly appreciated. Thanks in advance.
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IMHO this is somewhat offensive on behalf of the membership at large. There are many experts HERE willing to help as well.
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I'm an Expert!
This is very similar to the Kustom Defender with an added tone stack. I modded a Defender and added the tone stack and an MV. The drive was very susceptible to attenuation, (not sure if that's the best term), by turning the tone stack controls. Only full bass provided a nice loud sound. I may not have followed the instructions completely. While it only puts out about 12 watts, I've been told you should have a 50 watt speaker to handle the output. I don't know it that's true though.
There was a schematic floating around the Internet of the Defender. Very similar to yours. Here is where I got the mod instructions. kustom defender 5h many pics - MyLesPaul.com This will be a great start if it is your first project. Tell us about your experience with high voltage and safety precautions.
Ccat.
This is very similar to the Kustom Defender with an added tone stack. I modded a Defender and added the tone stack and an MV. The drive was very susceptible to attenuation, (not sure if that's the best term), by turning the tone stack controls. Only full bass provided a nice loud sound. I may not have followed the instructions completely. While it only puts out about 12 watts, I've been told you should have a 50 watt speaker to handle the output. I don't know it that's true though.
There was a schematic floating around the Internet of the Defender. Very similar to yours. Here is where I got the mod instructions. kustom defender 5h many pics - MyLesPaul.com This will be a great start if it is your first project. Tell us about your experience with high voltage and safety precautions.
Ccat.
I deal with them a lot and I know what they can do, they are specialized in guitar amps that is totally different from audiophile amps. I design guitar amps, I know.
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Hi Ricky,
This is also similar to a Mod-102 and a few others..
Have a look at those schems too. I would expect about 5 watts, maybe a bit more
Your output transfo needs to be rated to handle the idle current, and it's about 5K at the primary with an 8 ohm speaker. Little things to consider, a shorting jack on the instrument input, clean wiring, and also on the speaker jack some recommend a 220 Ohm across it or shorting..so if you turn on the amp without the speaker connected it won't blow the OT. Otherwise it looks good.
This is also similar to a Mod-102 and a few others..
Have a look at those schems too. I would expect about 5 watts, maybe a bit more
Your output transfo needs to be rated to handle the idle current, and it's about 5K at the primary with an 8 ohm speaker. Little things to consider, a shorting jack on the instrument input, clean wiring, and also on the speaker jack some recommend a 220 Ohm across it or shorting..so if you turn on the amp without the speaker connected it won't blow the OT. Otherwise it looks good.
I have what may seem like a silly question so please temper your vitriol. Just what are we trying to achieve in an instrument amp section that we don't pursue in a standard stereo amp intended for music playback? Please ignore the pre-amp and effects section, we're talking just the amplification.
Noted, so we want a more durable version of a home stereo amp. IOW, one that will tolerate mains variations, changes in temperature and a broad range of instrument electrical input better than a home unit but have the similar linearity and distortion characteristics. What I'm aiming to understand is if the goal with an instrument amp is to purposely introduce non-linear behavior outside of the pre-amp/FX section.
Note that you are thread jacking, but the OP or a mod have not objected so I will reply.
You cannot completely ignore preamp if asking for an analogy as that is an amplification stage.
There are 2 major differences in the typical electric guitar amp that distinguish it from a hifi amp. The first is the ability to amplify a low level & high impedance source to speaker signal level. The second is to add colour to the sound such as a overdrive sound, reverb etc.
In the case of a tube amp such as this thread the design typically attempts to be able to overdrive preamp or poweramp tubes to generate a dirty sound rather than mimicking that sound by other techniques.
Using a 5y3 would reduce the need for such a large amount of power dissipation by the pair of 5wt droppers. I'm thinking a single 5wt at 1k or so may get you there but I have not run any numbers.
The el84 can be run at higher voltage than "spec" as seen in countless guitar amp applications. A little more power and less resistor-heat would be the result. The cathode resistor in the el84 may need to be increased with higher plate voltage.
The el84 may idle at 12watts or so but, as mentioned, the output will be only a few watts.
The el84 can be run at higher voltage than "spec" as seen in countless guitar amp applications. A little more power and less resistor-heat would be the result. The cathode resistor in the el84 may need to be increased with higher plate voltage.
The el84 may idle at 12watts or so but, as mentioned, the output will be only a few watts.
I think Leadbelly said it well in his answer, and that is the case of looking at the preamp and power amp working in tandem. It's the type of non-linear behavior one needs to be careful with. It should overdrive gracefully, there should be a measure of clean non distorted sound at the lower volumes, but be capable of sounding good at higher than normal input signals. Even at 5 watt ''rated output" the amp could push out more at transients, so a musical speaker rated at 15W or 25W would be good in this case. You can overdive the output section at more tolerable level in the case of this 5 watt amp than a 50 or 100W one. In those cases more emphasis on creating dirty sound at the preamp side. If you want more dirty on the preamp side of this 5W, you can run a boost pedal, or use single tone control instead of treb-mid-bass for less signal loss at tone stack. Some small amps have a ''tweed style'' switch which will direct the signal to either single tone or TMB tone.. that could be fairly easy to do on this amp.
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