Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: reddead83 on March 05, 2019, 05:28:57 pm
-
I've been toying with the idea of making an EH-185 for awhile now. I've seen Pompeiis thread but I figured it would be fun to do my own layout more in the vain of a vintage style amp rather than a more modern layout. Can anyone check this for me please?
Thanks.
-
Anyone willing to give me some notes?
-
I don't understand the Tone network. It seems to run in a loop and would have no effect? Also 1K seems a mighty low value.
-
Pin 5 of both 6L6s is tied together on the layout. Not gonna make much sound.
-
I built a working EH-185 a while back, here's my layout. It worked great, it seems like there may have been one error though and i don't know if I fixed it in the layout.
~Phil
-
Sorry was distracted, missed your point you'd seen mine. :D
I'll take a second to review but sluckey already had some input.
~Phil
-
Sluckey I'll remove the jumper from the caps.
PRR 1k pot is an error. It should be 1M.
Thanks Phil. I would appreciate any notes.
Thanks guys.
-
Yeah PRR seems right there, on the original schematic the 'treble' pot is 1Meg not 1k. And the return from the pot should go to pin 4 of the PI, not back to the other side of the 750pF cap. One side (since it's a variable resistor it won't matter a ton which one) needs to go from the output of the 0.1uf Cap and the other should go straight to pin 4 of the PI V4. (or maybe just the other side of the 750pF cap on the board, since that's directly connected). It seems your 'orange' wire on the tone is what should move to either pin4 or the other side of the 750pF cap.
As Sluckey stated, you've got a jumper wire between the two 0.1 uf caps that output from the PI and that's got to be removed (the yellow wire). Or they won't give you any sound at the Output.
You also note a 750 ohm field coil. Do you have a field coil speaker? If not you'll want two 1500 ohm 20W in parallel to split the current load, like in mine.
Otherwise it looks good.
Edit: I had written this all up as you posted but am sending anyway, you've sorted some of them out.
~Phil
-
Thanks Phil I'll make those changes. Appreciate the help.
I don't have a field coil speaker so I'll be using the 20watt resistors as you stated.
I've seen other clones that use a choke. Did you use one on yours? Would you recommend using one?
-
Thanks Phil I'll make those changes. Appreciate the help.
I don't have a field coil speaker so I'll be using the 20watt resistors as you stated.
I've seen other clones that use a choke. Did you use one on yours? Would you recommend using one?
I do not. I don't know if a choke at around the 750 ohm rating would provide a more 'original' tone, but with the purely resistive load it sounds incredible to me.
~Phil
-
I don't understand the Tone network. It seems to run in a loop and would have no effect?
A bunch of parts, connected at a single node, does about nothing.
Phil has the right connection: "the return from the pot should go to pin 4 of the PI, not back to the other side of the 750pF cap".
-
Thanks Phil.
PRR so it shouldn't connect to the 100K that goes to ground and the 750pF cap junction and then to pin 4 of the PI tube? I see the mistake of connecting to the coupling cap. I was watching Phils videos and he originally had the return of the tone connected directly to pin 4 and it didn't work until he connected the return directly to the 750pF cap and then to pin 4 of the phase inverter tube.
-
I think that was because of the error i had, and I think i remember what it was now. I have the pin 4 of the PI connecting to the treble wiper, but I didn't also connect the other side of the 750p cap to the same pin and when I did that, it sorted out the problem.
If you look at the schematic, it shows four connections at that point.
1. the leg of the 750pf,
2. the leg of the 100k resistor
3. the wire to the Treble Pot
4. the grid (pin4) of the 6N7.
Basically yours is wrong because it connects pin 4 to the wrong side of the 750pF cap.
~Phil
-
Makes sense now. Thanks.
-
@reddead83, would you have that layout updated/fixed? Did you end up building it? I want to build one and getting a validated and ready board layout would save me a lot of work and time. Thanks.
-
Replay #4
Franco