If I used loop feedback, I'd keep the 6SL7 because I'd need as much open loop gain as possible to benefit from the loop feedback. The "reylon" uses a pentode input for this reason I believe.
I would use the ultrapath feedback technique on the output tube to improve bass response and lower bass distortion.
If I had the money, I'd consider getting an output transformer that had a cathode feedback winding.
I would use the ultrapath feedback technique on the output tube to improve bass response and lower bass distortion.
If I had the money, I'd consider getting an output transformer that had a cathode feedback winding.
Look to the Pye Mozart for inspiration, transformer secondary in the EL34 cathode circuit works really well.
Change the coupling capactor?
If you indeed have a solon coupling capacitor, you can do a lot better than that, although it probalbly is not the sole reason why you don't like the sound.
Retsel
If you indeed have a solon coupling capacitor, you can do a lot better than that, although it probalbly is not the sole reason why you don't like the sound.
Retsel
The normal bias resistor for an EL34 with a plate voltage of around 450 is 470 ohms. You will need a 10 watt resistor. A 25 watt is over kill, but will have things running cooler. If you are pulling around 30 volts across a 470 ohm cathode resistor, you are where you want to be. Around 25 watts of plate dissipation at idle. This is where I run my single ended EL34 guitar amps as well as my push pull hifi amps. The EL34 is good to about 28 watts plate dissipation before the plates start to glow red. Spec for the EL34 is 25 watts. An SE ultra-linear EL34 amp will deliver around 10 watts. In pentode connection, you can get 12 - 15 watts. In triode mode, you are looking at around 4 watts. Of course, this depends on plate voltage. Your schematic says 380. I run almost 100 volts higher in my amps. The 6SL7 makes an excellent driver for this tube.
You run at 480V to your anode plates. Any difference with that voltage as compared to 380V.
Yes, loop feedback is great for reducing distortion, particularly from the transformer if you take it from the secondary, but, also, feedback controls gain, so that it does not change with aging of tubes (up to a point of course) and so that the gain in each channel of your stereo will be the same. If you have different gain in each channel, then your image will shift left or right. Also, with feedback you do not need to buy expensive matched tubes. It also reduces output impedance so that your bass response of your loudspeakers will sound better because the amp's damping will be higher. However, there can be stability problems if you have too much phase shift and you try to apply too much feedback. You can't just use it blindly without proper measuring and testing.
One way to reduce phase shift in this amp is to DC couple the input tube's plate to the output tube's grid. You will have to make other adjustments of course. Find a way to get rid of C2 in other words.
Yes there is a difference at the cathode. You could probably go with a 440 ohm cathode resistor with 380 volts on the plate. Remember, you must subtract the cathode voltage from the plate voltage when making plate dissipation calculations. Also there is the dissipation of the grid. In the EL34, it is higher then most tubes of that size. This tube has been used triode connected, but I have found no improvement in sound over ultra-linear. The Dutch Phillips company designed this tube for audio applications in the 50's and specifically for an ultra-linear type loading. The EL34 is probably the best performing tube I have ever used in an ultra-linear circuit, be it push pull or single ended. The single ended amps I have built around this tube all have no feedback and all sound great. Even the bass is respectable. Obviously the push pull amps with feedback have a bit tighter bass, but the SE amps are no slouches in the bass department. I like the EL34. It is my favorite output tube because it just plain works and sounds great. It is fairly forgiving with respect to biasing. Just make sure it does not red plate and you'll be OK in most cases.
I got what you meant. EL34 specification also stated no more than 500V on the anode plate otherwise it may red plated. I agreed with you this tube was one of the best and commonly used in audio circuit.
Yes I have just modified my SE EL34 that we built in the thread a while back.
It has the secondary feed back with a 317T in the cathode.
Ie cathode cap to OP secondary and 317T as CCs with 15 ohm 5 watt set resistor straight to ground. So I can plug in EL34/6l6/KT66 etc..😀
I was not sure how it would sound but its been on for about 6 hours now..ie still playing and its staying on for a while longer if you know what I mean.
Regards
M. Gregg
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No its just a standard UL 2.5K-8 Ohm.
It was a reply to Toprepairman..😉
Regards
M. Gregg
I see I understand what you mean. I will look for your thread. I think you have mentioned it on your thread. Thanks.
Been reading {Hmmm bad thing} and it says the EL34 is a Pentode valve and is not a Triode so leave it as god intended a "Pentode" So I will try it set mine back to Pentode to see if much difference can be heard?? any guru out there can asure me Triode is fine no problems keeping it Triode?
You can use EL34 in triode and "True triode".
The power is lower in Triode.
A few things to try..
I would probably put a 1K on G2 if you are going to switch.
NB on the circuit diagram its not a good idea to have the grid of the first tube dependant on the volume control wiper for a ground connection. Put a 1Meg or 470K from the grid to ground. you could also get grid current that will damage the volume control try a 10K in series with the grid from the volume control (100K).
Change anode resistor on the SL7 to 150K and try it again.
Without FB I guess you will have loads of 2nd harmonic..
The other thread..
http://www.diyaudio.com/forums/tubes-valves/179200-any-thoughts-circuit.html
Regards
M. Gregg
The power is lower in Triode.
A few things to try..
I would probably put a 1K on G2 if you are going to switch.
NB on the circuit diagram its not a good idea to have the grid of the first tube dependant on the volume control wiper for a ground connection. Put a 1Meg or 470K from the grid to ground. you could also get grid current that will damage the volume control try a 10K in series with the grid from the volume control (100K).
Change anode resistor on the SL7 to 150K and try it again.
Without FB I guess you will have loads of 2nd harmonic..
The other thread..
http://www.diyaudio.com/forums/tubes-valves/179200-any-thoughts-circuit.html
Regards
M. Gregg
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