Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: roarshock on May 19, 2021, 07:39:57 pm
-
Hello all,
I am working on a project and could use your input. If you are reading this, you know more than me. I am trying to cobble together a small amp with harmonic tremolo and reverb using schematics from several sources. Are you cringing yet? To further complicate things, I am planning on using a power transformer pulled from a large phono/ stereo (motorola HS-780) which has a different secondary voltage (260-0-260) than the power transformer of the preamp/power amp that I am basing this project on, the ubiquitous 5F2-A. My PT also uses a dedicated 6v winding for a EZ81 instead of the 5v winding for the 5Y3 that the 5F2-A.
Questions:
1) Do I use the filter cap set for the regular 5F2-A( 2x16uF and 2x8uF), or because of the differences in PT/ rectifier, should I use the filter cap set from the HS- 780 (4x40uF), or something altogether different? ANSWERED, sort of. See post #6.
2) Due to the difference between the HS-780’s and the 5F2-A’s PT secondary voltage, I changed some of the voltage dropping resistor values and placements to approximate the voltages for the 5F2-A. I am off there?
3) The harmonic tremolo is from a 6G5 and I changed the first voltage dropping resistor to better match the voltage from my PT. Am I off there?
4) Do I still need the 20uF caps for the tremolo as the 6G5 has them?
5) Should I incorporate the reverb and or tremolo into different parts of the 5F2A circuit?
6) What else needs correcting?
I’d love answers to any and all. This is my first schematic drawing, so pardon the poor layout/ numbering of resistors/ caps/ tubes. I have a lot to learn with DIYLC! I do plan on adding some other things to the circuit, but I would like to know if I have a viable platform first.
I’m a bit of a paint-by-numbers kind of amp builder this far, but I am continuing to learn things as I plan this next build. I have built a deluxe micro ala RobRob so far and I know that this is a big step up in terms of complication. I just really like reverb, harmonic tremolo, and tube amps and I haven’t found an all-in-one solution yet.
Thank you for your time and thoughts!
-
Welcome aboard.
It would be really helpful if you rendered your schematic from diy-lc to a pdf, png or otherwise viewable format.
Your project sounds ambitious!
-
Thanks acheld!
So far the conversion is coming through a little fuzzy, but I've added it to the original post and will look into other ways of converting the file for ease of use. Yes, this is ambitious, but it will be my summer (and maybe fall) project.
-
6V6 grid has no path to ground.
-
Sluckey, I am humbled your eyes have seen my work. I just stumbled into your schematics page and made an adjustment to where the harmonic trem connects to the high voltage. I had not seen a schematic with voltages and your page really helped with that hurdle. Thank you for that! I have updated the 1.1 schematic to 1.2 to reflect that the 6V6 gets a path to ground. I have a feeling there are more errors and or things to consider.
-
I keep doubting my own ability to learn enough to do this on my own, but I am surely open to trying to figure this out with a little help. I know I am way over my head with the design part but fortune favors the bold (who looks things up).
Question 1 answered?
Filter cap network: I did a quick perusal of a Merlin Blencowe’s page today and although previously I told myself I wouldn’t be able to think this through, (there are many new terms and symbols for me to wade through) I gave it some effort. I looked at the data sheet for an EZ 81 and learned where to find it’s max value for reservoir cap which is 50uF. So, to be safe, I’ll go with a 40 uF 450v ( or something near that uF) for the reservoir cap. After that, it sounds like Fender’s filter cap network is a fine choice. So 40uF, 16uF, 8uF, and 8uF. If you have more helpful input, I am all ears. What an adventure so far! I’ll update the schematic to reflect the change.