Bogen Challenger Cha33 Conversion to Cascaded Plexi (AFD)
Вставка
- Опубліковано 8 вер 2019
- In this video, I show how I converted an old Bogen Challenger CHA33 Tube PA amp into a loose interpretation of the Cascaded Plexi (AFD style).
*If you have interest in doing this type of conversion and want to know more, please contact me directly, as there are many details that I have not included in this video, but will gladly share. jloewenheim@gmail.com
Schematic can be found here: sites.google.com/site/jloewen...
Featured are some upgrades that mostly are a result of the great webpages put together by Rob Robinet. First and foremost is the Cascading of a cold clipper pre amp stage. Also, adding a pre-phase inverter master volume, Type 3 post PI Master volume, making the bias adjustable, and having a 3-way negative feedback switch.
Things not mentioned:
-The adjustable bias setup: see Rob's page here: robrobinette.com/Generic_Tube...
-Shielded RCA type cable is used throughout to reduce noise from volume pots
-Wiring is point-to-point
-Input grid leak is 33K
-Screen resistors are mounted directly on chassis
-I replaced the incandescent pilot light with a 12v panel mount LED (no rectification needed)
Also if you like my channel and this video on amps, I suggest subscribing to the following awesome channels:
-Uncle Doug: / @uncledoug
Uncle Doug has tons of other videos, probably the best teacher on UA-cam regarding amps
-The Guitologist: / @theguitologist
Brad runs an all-around great channel, loves to work on wonky stuff as well as standard guitar-related gear.
-D-lab: / @d-labelectronics
Terry is likely the best electronics technician working to repair tube amps on YT.
Related links:
Rob Robinette
-Safety! Rob's word on capacitor discharge and lethal voltages in tube amps: robrobinette.com/Tube_Amp_Saf...
Rob's site is likely the most comprehensive resource regarding classic Fender amps, and now amps work.
-59 bassman site: robrobinette.com/5F6A_Modific...
-Uncle Doug on Biasing: easiest way to really understand how biasing works
• Biasing Single-Ended A...
• Biasing Double-Ended A...
• Biasing Double-Ended A... - Навчання та стиль
![ОРБАН приехал к ПУТИНУ и "отчитался" о поездке в Киев 😁 [Пародия]](http://i.ytimg.com/vi/_0ukDovOWq8/mqdefault.jpg)
Super cool. My grandpa passed away and left behind a CHA33, and I'm exploring converting it into a guitar amp, so this was so helpful.
This seems pretty advanced - do you have any tips/recommendations for a beginner?
@@d.lauzon I have 2 recommendations that are a bit easier. First, you can leave the circuit fairly intact, simply replace the capacitors, and then revoice a few of the stages to be a bit more guitar-friendly. This only requires changing a few resistors and caps, while otherwise leaving things in stock form in terms of layout.
The other idea is to build a more common version of the 5f6a or marshall in a different chassis, then use the tubes and transformers from the bogen chassis in a manner that you can easily reinstall them in the future if you like. Use these for the build
Either way, please email and we can discuss further offline. username@gmail
That sounds nice.
I dig it. Did something similar recently and used 270K/470K in the voltage divider. Insane gain.
Thanks, hope you are enjoying yours
@@jloewenheim One key to using old PA heads for guitar is to use pedals! EQ, Comp, Verb, Chorus, distortion, sweetner, an yer off to the races!
I have one of these amps and quite a few mods to old pa amps. What you have done is truly wonderful sounding. Would you consider doing a mod/build like what you have done to yours? I love to contact you if possible. Thanks
Thanks for the compliments. Yes, look forward to discussing with you more.
Killer Amp.!
Thanks for publishing the schematic. I have two CHA 33's and two CHA 20's (6V6) I've converted one CHA 33 (6L6/EL34 w/bias/balance) to an AB763 Bassman w/LTP PI and another half 12AX7 gain stage. The CHA 20 is now converted to a AA764 Princeton type head with a Cathodyne PI and a few tweaks. I think I'll give your AFD schematic a shot. I only use point-point and they usually look very clean. I've done about 50 PA/Hi-Fi conversions and it's a blast. Just finished converting a blown out solid state 2x 10" combo to a Princeton.
Thanks again to you and of course Rob R.
Thanks for the note. I look forward to seeing what you put together. I definitely would do slightly cleaner as far as layout if I were to go back again.
This schematic looks eerily similar to some Lectrolabs that I've seen; were the Bogens built in the Chicago area?
I could be wrong, but I think to this day Bogen is in New Jersey. I think that type of circuit with a Bax TS and such were fairly common for many a PA and other clean amps of this era.
Great work. Real good stuff. In the demo the plexi mode sounded like it's just barely on 4 on the volume and not rocking.. But I get it. In cascade mode you can't turn everything up to 10. When going between modes one has to adjust the volume /gain levels.
Just for other guys who maybe wonder why the plexi mode sounds weak.. It's just not turned up much.
Thanks Joe, I should have clarified a bit. The pre amp vol and pre PI master vol (JMC800 style) were both at about 5 (out of 10), then the Type 3 MV was at about 40%. Wattage for this amp is somewhere in the 45-55 range at full vol. The studio where I recorded this wasn't big enough to push the amp to that level.
@@jloewenheim would be interesting to see how a plexi or similar amp responds to a paraphase inverter. I love the Gibson Ga6, ga20T and Ga40 who all have a paraphase. I think no one tried a plexi preamp with paraphase inverter.. Maybe for your next build. :)
Or a PA amp into a GA6 or tweed 5D3.. That's what I want to learn. Many old PA amps out there cheap.
@@BlackBalloonGraz Terribly! I've converted about 50-60 Hi-Fi's including Bogen CHA 33 (2x6L6) and two Bogen CHA 20's (2x6V6) I can wire up a point to point Cathodyne/Paraphase in my sleep but for some reason I have a hell of a time laying out/wiring up a Long Tail PI. To make a decent sounding 6L6/EL34 rock amp you need the Long Tail PI. Without it it will have very low volume and gain with 3 gain stages (last 1/2 of second 12A*7 is used for Cathodyne PI) I've had fantastic results with Push-Pull 6V6, EL84, (6AQ5's are my favorite) with a Cathodyne PI but not once with 6L6 or EL34's. If I could figure out how to wire a Long Tail up I'd have another dozen working 30-50 watt heads. I just can't get it from paper to the chassis.
@@williswet I agree that LTP can be a bit of a pain to do PTP. I have built a few amps where this has been a challenge, if you like, feel free to email (username @ gmail) and I can share what I have learned.
@@williswet you can always just do a mix of point to point and tag/turret board. I’ve done that in a few different amps. I know a lot of guys love p2p but I’d be very surprised if they (Ken Fischer not included)could a/b two unfamiliar amps in a blind test. The point is a working amp. I love seeing both as long as they’re well done. LTP is pretty tidy on a board.
Getting ready to convert one of these. Decided to go for a Bassman but might leave it cathode biased with large value bypass cap to mimic fixed bias feel. Don’t know yet. Might use the fixed bias part of your circuit if you don’t mind. ✌️
Good luck, feel free to reach out if you need any advice (username @gmail.com). Remember that there is a lot of juice in that power transformer (on today's mains), so you may need to play around with the cathode bias resistor value if you go that route.
@@jloewenheim I don’t think I’m sticking with the two 5y3’s. I think we’ve moved past that as a society;-). Solid state diodes and a resister for a bit of sag makes more sense I think. I’m tempted to keep the PI paraphase just because the bassman did alright with one for a while. The Bogen should be a nice change of pace from Hammond and Roberts reel to reel amps I’ve done for the past few months!
@@williambock1821 OK, so since this build, I have done a few more conversions, and my honest advice is as follows (conversions can be a pain and frustrating): Unless you are really determined to figure out how to keep the Bogen chassis and look, you pull the transformers and tubes, then use a more Fender/Marshall approach on the chassis and board. This gives you two advantages: first, you can now always drop the transformers back into the original if you want to sell it as such. Second, and more importantly, the fender style eyelet board (turrets too) will allow you to be very organized and methodical about your build, as well as, give you the room necessary for controls and other circuit options that go beyond what Bogen did.
As for your rectifier (despite what Mesa advertises), the dual 5y3s make it run very hot, so there are advantages to going SS. At some point, I will put on some videos where I have started to use a VVR circuit. This allows those old PT's, which on modern voltages, often have secondaries around 400v, be used closer to the voltages we know. Additionally, it allows you to go SS rectifier without needing to rely on sag.
@@jloewenheim Thanx for the input! I’ve done four or five conversions with VVR’s and when they work well they work VERY well. Some circuits(I’m just talking about cathode biased amps) just get too fizzy to really get much use from them. I’m sure they could be made to sound better if I had more experience. So far , I can’t narrow the variables down to what makes a VVR sound too fizzy. Some sound great at low voltage levels and some sound like a wet fart,lol! The Roberts reel to reels sound great with them if you do a one 12ax7 going into the El84 like a 5 watt version of a Marshall 18watt circuit. The actual 18 watt lite 2b circuit in a Hammond Ao35 sounds good too. Not much luck with Hammond Ao44’s though regardless of the conversion (tried 5 different ones) done. I’m tempted to try one on the challenger. I have all the components on hand for exactly ONE more VVR!
@@jloewenheim I wound up turning it into a 5e3 with VVR and bias selector switch for 6v6/6L6GB’s. Replaced the burnt out OTX with a brand new 25 watt Hammond 1650F. Wiring the impedance selector was…interesting! Used F&T for B+filter caps and Jupiter everywhere else. Well,a Sozo silver mica was used for the bright cap. Wired it all point to point with creative use of a few tag strips. It’s the best sounding amp I’ve built out of around 25 so far! I wish I could keep it but it’s already paid for. I’m looking for another Cha 33 for myself! Just as an FYI, the cathode resistor needed to be upped to about 700 ohms for 10-11 watts (about 80% ) of plate dissipation for 6v6’s. The 6L6 GB’s needed 330 ohms for the same percentage of dissipation. Again, this is a 5e3 build.
Just picked up an old Bogen J330 projector amp conversion but can't seem to find much info on it Supposedly cascaded channels for a warmer sound Any thoughts ?? Thanks Good stuff 👍
do you want to connect via email? my username at gmail.com
@@jloewenheim sorry for the late reply Yes will email Thanks
Great sound...please send preamp with 12v from guitar pedal slashs tone schematics?
Thanks. There are no pedals in use here, basically a JTM45 schematic with a cold clipper stage cascaded in. I'm not quite sure what you are asking, please let me know.
Ya screwed it up dude, they sound way better stock than this!