AX84 High Octane build

[Paul1453]

I'm going to try to build the AX84 High Octane into my old Bi-Ampli radio chassis this weekend.  My PS is different and I'm learning to use the PS simulator.  attached is a pic and my .psu file (.psu won't upload).  The PT has a jumper to change for different voltages.  When I set it to 127 I get 6.1VAC for my heaters and 270VAC going to my EZ80 rectifier.  I've got a new 80,60,40,20 uf 350V cap can I intend to use.  I used the PS simulator and made some changes to get simulated voltages very near what is shown on the schematic.  I changed R1 from parallel with C1 to 1.4K and in series with R2.  I've got 80uf after R1 then changed R2 to 400 ohms, C2 is now 60uf, R3 1K (same) C3 40uf, R4 10K (same) and C4 20uf.  When using the software I made the load constant current at 40mA and then ran the simulation and got voltages very close to what is called for.  The software gave me a warning with using this load, and I found that if I changed the load to resistance at 200 ohms I got the same voltages but no warning messages.  This is the 1st time I've tried to use this software, but I think I did OK and have managed to use it to find the proper modifications to the components to get the voltages I need.  B+1 @ 259,  B+2 @ 250, and B+3 @ 234.  Would you mind taking a look and seeing if you think this will work?

I don't have all the pots I need for the tone stack, so I plan on dropping it for now and simply replacing it with a .022uf cap between R11 and the Master Volume for the time being.  That's the same value cap used in the preamp stages.  Do you think that is OK, or would you suggest a different value cap be used here?  I plan to try different values here if I don't like the tone since I'm not using the stack for now.  I'm thinking that value might be pretty bass heavy.  If so would the 470pf from the top of the TS be a good try to remove some of the bass?

I appreciate your feedback and any tips or suggestions.   

[PRR]

> The software gave me a warning

What did that warning say? "Do not drink"?

[DummyLoad]

what output tube does the radio use?


--pete

[Paul1453]

> The software gave me a warning

What did that warning say? "Do not drink"?

I think the message was something like " A value was exceeded 5 times by .083652 seconds".  When I changed the load to resistance and not current the message did not appear.

I haven't had a drink in a few months.  If this build goes together as planned, and sounds as good as I hope it will, I'm thinking a celebration drink will be in order.   

[Paul1453]

what output tube does the radio use?


--pete

The radio came with a full compliment of Philips MiniWatt tubes made in Holland in the late 40's or early 50's.  9 total, all good except for the magic eye tube I think.  It had the EL84 in conjunction with an EL86 as output tubes.  I plan on using my Sylvania EL84 at first to work out any bugs, and then trying out my MiniWatt and Bugleboy EL84s to see if these premium tubes are all they are said to be.   

The EZ80 has a unique perch mounted horizontally on top of the PT.  I've decided on how I want the tubes laid out using the existing holes.  EL84 kind of in the middle at the far end of the chassis from the PT.  It doesn't look like any of the existing holes match up for mounting the OT, but it's going on the very far end from the PT somehow near the EL84.  The 2 12AX7s are going in the back row with one on each side of the approximate middle line.  The new sockets are mounted with the heater wires twisted and soldered on.  I'm using the old selector tab levers as the On/Off power switch.  Press down on any selector lever and it stays down and turns on the power.  Press down on the far left lever and it pops up any of the other levers and turns the power off.  Except not always, sometimes it pops the other levers up but doesn't fully disengage itself and turn the power off.  I'll have to work on that.  The 12AX7 tubes are mounted in their fully shielded sockets and all the tubes light up and warm up as they should when one of the levers is depressed.

[PRR]

> message was something like " A value was exceeded 5 times by .083652 seconds".

I bet it was more like the one attached.

Many computer error messages are stupid.

Duncan's are very specific, and TELL you what the problem is.

[Paul1453]

I'm on my Linux computer so can't run it right now.  In the morning, on the win-doze machine, I'll change the load back to constant current and take a snip-it picture of the error message to post.  I thought it was warning about the transformer, but I'll know for sure in the morning.  Other than that, those mods were pretty minor and I wouldn't expect them to overburden my transformer or rectifier.  But what do I know?  I'm just an out of practice repair tech trying to learn a boatload of new information.  It's an extremely simple PS circuit, and with the help of the software I'm pretty confident those changes are going to put me in the ballpark of voltages that will work.  Unless someone like you PRR, tells me otherwise.   

I'm not sure I changed the transformer values in the software correctly, but I think that is the only place where my inputs could have screwed things up.   

[Paul1453]

Some pictures so far.  Don't laugh too hard, OK?

[Paul1453]

HO_1 shows pretty much where things fit.  The OT looks like it has two holes that will work to mount it there.  The old cap can was located where the new one is sitting now.  I wanted it to go over next to the PT, but the holes will have to be modified for it to go there.  I wanted to make a small PS board that would go on the bottom side over there and have another main circuit board that mounted topside for easy connection to the pots (which I haven't figured out how I want to mount yet).  The radio case only has holes for 2 pots to stick through on the front, and even dropping the tone stack I've already got 3 pots.  If or when I add the tone stack I'll have 3 more so some will obviously have to go on the back, unless I drop the original front glass plate and deviate far from it's original vintage radio look.

Can that Hammond OT have a 4 ohm speaker connected in the front, and with the other jacks mounted on the back and have an 8 or 16 ohm cab connected simultaneously?

HO_2 shows the transformer's voltage selector and the horizontally mounted EZ80 regulator, with my 3 prong plug and fuse modifications added.
HO_3 shows the wiring on the bottom so far.

Well what do you think?  Critiques, comments, suggestions?

[Paul1453]

Since I'm bearing my soul for all to see I might as well post the pics from last weekends successful but incomplete 6V6 PP build project and keep the laughter going.   

This ones kind of in the transformation stage from bench assisted configuration and design to reinstall in the original housing and clean her up stage.  It's a fully functional Gibson BR-6F clone with only one input jack and an OT substituted for the field coil speaker.  It's still dependent on my bench PS because I think I jacked it's PT when trying to follow the schematics design of grounding the heaters CT.  I think I am going to just go with the 100 ohm artificial centertap in the future even when the 6VAC has a CT to avoid having any more PT catastrophes.   

She's nice and quiet, no hum.  There's no tone adjustment and she seems to develop some kind of high frequency whistling feedback at pot levels above 8.  Back her off to 7 and it goes away and she's nice and quiet again.  The gear she came out of has a 12" field coil speaker that I'm not sure of it's status and if she would work well as a guitar amp speaker.  Also there is plenty of room in her chassis for me to go with a more sophisticated design like Doug's Tweed Deluxe or something else.  I don't think I'm quite satisfied with the Bronco's simple design and sound yet.  This one has lots of potential to make into a really nice sounding Rock'n'Roll guitar amp.  But it does work now just as it is.     I still need to figure out what I'm going to do about her PT so that will have to weigh in on the design I settle on.

[Ed_Chambley]

I don't have all the pots I need for the tone stack, so I plan on dropping it for now and simply replacing it with a .022uf cap between R11 and the Master Volume for the time being.  That's the same value cap used in the preamp stages.  Do you think that is OK, or would you suggest a different value cap be used here?  I plan to try different values here if I don't like the tone since I'm not using the stack for now.  I'm thinking that value might be pretty bass heavy. 

I build a lot of amps without tonestacks, especially low watt amps that I want to max out the touch sensitivity.  I do use rotary switches to change coupling cap values since I prefer to use low output Single Coils in my Telecasters, but also have a Baritone PRS with higher output PUPS.  Sometimes I may use 2 rotary switches and pots for changing bypass values.

[John]

I build a lot of amps without tonestacks, especially low watt amps that I want to max out the touch sensitivity.  I do use rotary switches to change coupling cap values since I prefer to use low output Single Coils in my Telecasters, but also have a Baritone PRS with higher output PUPS.  Sometimes I may use 2 rotary switches and pots for changing bypass values.

Same here (well, not a "lot"). In fact,  my 20 watt doesn't have a TS either. I used a rotary switch with different K caps on the input tube (which is paralleled). I love it, for me.