Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: nastyoldtech on July 30, 2009, 12:02:27 pm
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If you have some cool modifications for these amps post them. These J-20's are 6G3 clones for the most part and both can benefit from improvements.
I have a J-20 that I've been modifying over the past couple weeks. My goal on this is to keep it simple, retro, and get as much out of it as I can. So I came up with a plan to convert it into a 18W Lite II-6V6, 5G9 Tweed Tremolux, Hybrid Brown/Blackface Deluxe, and a high gain 18W Lite II-6V6 all with a few switches. And it's all pretty simple and straight forward. Not at all being what it might look like at first glance like some over the top project. There is some compromises, each one is not identical but pretty close to the original getting a in the ball park feel of the original amps.
1.) The 18W normal channel (Lite II) and the 5G9 are very similar in topography. Of course you have that tremolo section with the 5G9. If you look at the J-20 you have that extra gain stage V2b that actually attenuates the signal pretty well. If you move that over into the tremolo section and with a few value changes you basically have a 5G9 and it really opens up the amp, louder with more headroom. By beefing up the preamp section by tying the plates together and jumping the channels you get a nice gain boost and up the volume something that looks like it was sorely needed with the 5G9. You still get major amounts of headroom like the 5G9 but the amp is much louder. This also leaves an extra input jack for the gain control on the mod below. I lowered the preamp voltages by rasing the J-20 R14 resistor from 10k to 27k. It helped brown it out and make it less sterile sounding.
http://www.prowessamplifiers.com/schematics/ampeg/Ampeg_J20_Jet__Current_Production-fender_6g3_brown_deluxe_Clone_hand_wired_J_20_Jet_.html (http://www.prowessamplifiers.com/schematics/ampeg/Ampeg_J20_Jet__Current_Production-fender_6g3_brown_deluxe_Clone_hand_wired_J_20_Jet_.html)
http://i939.photobucket.com/albums/ad240/nastyoldtech/tremolux_5g9_schem.gif (http://i939.photobucket.com/albums/ad240/nastyoldtech/tremolux_5g9_schem.gif)
http://i939.photobucket.com/albums/ad240/nastyoldtech/18wattLite2b.gif (http://i939.photobucket.com/albums/ad240/nastyoldtech/18wattLite2b.gif)
2.) By setting up the tremolo to 5G9 Tweed Tremolux specs you get a very sweet tremolo. I had to do a few modifications to it that I'll post my final findings a little later but it's much thicker than the stock J-20/6G3 tremolo. At fast speeds it almost double stutters. Listen to Link Wray's 1958 studio recording of "Rumble". He used a Tremolux on that that, very retro sounding. On slow speeds it's very swamppy like something off an old CCR album. The stock J-20 tremolo is thin by comparison. Tremolo is not for everyone so if you're not into it that extra triode could go to other uses like an extra gain stage or buffer for an effects loop etc. But with this mod I'm doing in #4 I don't think you'll need an extra gain stage. :angel
3.) I put the NFB loop on a switch and changed up the values to blackface deluxe spec values 820/47 ohms removing that C10 cap. The new values improve its performance and keep it clean higher up the dial. Just remove C10 and change R21 to 820 ohm and R16 to 47 ohm. Setup your NFB switch so that it grounds that juncture of R21, R19, C11 and R16 to ground. This will disable the NFB and also switch the PI tail to ground. In the PI I upped that 10k resistor to 22k. I also changed R22 from 82k to 100k for better harmonic distortion.
4.) I'm going to wire the V1 triodes to switch between parallel and cascaded gain stages with a gain control. In cascaded mode combined with the blackface deluxe style output section and NFB loop it will be a pseudo brown/black deluxe. I'm thinking of adding a switch idea I came up with in addition to that to either tap the signal from a voltage divider network off the plate of V1b in cascaded mode like the brown deluxe or from the plate like the blackface. I have to see if I like it and if it would be worth the space of a switch. I might have that parallel/cascaded mode on a remote relay of some sort to switch that in as a gain boost for live work.
5.) VVR (variable voltage regulator) to adjust voltages between Tweed and 18W/Faces specs and allowing you to play at lower bedroom levels.
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6.) Finally I came up with this switch idea to switch between fixed bias and cathode bias but to also switch in the values needed to get 18W crunch from the output section. When in fixed bias mode those extra 430K resistors are switched in parallel with R32/R33 getting you your max (that we can do) fixed bias grid leak resistor value which turns out to be about 215K in this case. When in cathode mode those 430K resistors are switched out giving you 430K for some Marshall style crunch. Switch the preamp to cascaded and you have some high gain Marshall style crunch.
I'm planning on putting this on a rotary switch to be able to select different combinations of grid leak values in cathode bias operation. One I can think of would be a more tweed value of 215k (220k) in cathode operation for a touch of 5E3 Deluxe.
http://i939.photobucket.com/albums/ad240/nastyoldtech/fixed_cathode_switch_final.jpg (http://i939.photobucket.com/albums/ad240/nastyoldtech/fixed_cathode_switch_final.jpg)
Those are some of the mods I've done/process of doing. They actually are pretty simple and don't take up a lot of space or mar the look of the amp. Post what ever else you can come up with I would like to hear what you got and I would really appreciate you input and ideas or any questions you have about what I've implemented.
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A forum member sent me this. It's brown deluxe clone with a bunch of mods. Looks like some of those might be a pretty cool addition to a J-20, 6G3, AA763 or AB763 build. :undecided:
http://i939.photobucket.com/albums/ad240/nastyoldtech/AllenHotFudgeWNutsLayout.jpg (http://i939.photobucket.com/albums/ad240/nastyoldtech/AllenHotFudgeWNutsLayout.jpg)
Might someone have the schematic for this one?
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If you have some cool modifications for these amps post them. These J-20's are 6G3 clones for the most part and both can benefit from improvements.
I have a J-20 that I've been modifying over the past couple weeks. My goal on this is to keep it simple, retro, and get as much out of it as I can. So I came up with a plan to convert it into a 18W Lite II-6V6, 5G9 Tweed Tremolux,....
Hey, Nasty, I too have that amp, wasn't bad stock but past 7 the break-up was a little raspy and floppy. I did the 18 watt Litellb mod to the preamp and also disconnected V2b, big difference in the distortion, nice and clean and breaks up smooth now, I also put a switch on the NFB to turn it off, I'll have to change the resistors like you did.
Attached is a copy of the Litellb schematic I got the preamp from, not too complicated and also a layout of the J20 board, numbered like like the schematic you posted above. Let's make this baby sing.
I got the amp, for $300, it's all PTP, tag bd, handwired in China I guess but good quality. You'll find them at Musicians Friend for $800 but ebay has them for around $400. Has a big alnico 25w speaker, all pine construction, and looks reto just like the real deal, a steal IMO :wink:
I want to do the buffer on the tremolo you mentioned with the open half of V2b the litellb mod gave me, any info to share?
the dude
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Hey Dude,
This is what I got for the 5G9 tremolo section and how it compares to the J-20 in this circuit.
The 5G9 has a cathode follower buffer that helps make the tremolo more robust sounding. I think it's there to prevent loading which I think attenuates the tremolo circuit when it is not in place. There is also that mystery .022uf cap I marked as N/S on the J-20 layout.
That N/S cap I believe is an additional forth CR filter. I could be wrong I know little about tremolo circuits but I’m guessing that it is. When that cap is removed the effect is not as robust.
I have built the original 5G9 tremolo section into this amp exactly the way it’s shown with the same voltages. It might be due to the higher voltages and bias for the 6V6’s but the effect was not like recorded versions I have heard of the original 5G9 or even the 6G16 which is a similar tremolo but at higher voltages. I replaced that 1M resistor that’s just after the intensity pot and changed that to 220k as is a suggested Princeton Reverb mod to up the effect on those models. It upped the effect quite a bit but I got a bad ticking noise. That 1M in the 5G9 schematic is way too high a value btw. I personally think Fender might have thrown that on there to prevent RE'ing or changed it later down the road.
I looked at other Fender tremolo amps of the period and found that the 6G16 has that N/S .022uf cap. I figured they must have added that to rid the amp of that same ticking issue. I added it back in and low and behold not only was the ticking gone but the tremolo got really thick and sounded just like those old 50’s recordings with Tweed Tremoloux’s. So good, so good. Maybe one of the best tremolo’s ever put in an amp.
Anyway this is what I did (I’ll put up a layout down the road but this is for the impatient).
http://i939.photobucket.com/albums/ad240/nastyoldtech/Tremolo-Section-Final.jpg (http://i939.photobucket.com/albums/ad240/nastyoldtech/Tremolo-Section-Final.jpg)
There's a footnote in there about leaving the said values and upping that added resistor. If you have the time try both and tell me what you think of each. :undecided:
Just a heads up, with the preamp setup like it is and in fixed bias it's actually more a 5G9 than a 18W lite. Put that cathode switch on there and you'll loose the mile high headroom and it becomes a 6V6 18W Lite. But the Devil will get'cha, God rest your soul. :angel
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Thanks for the trem info. :smiley: I have managed to do a few mods that I like.
I tied the two lugs of the trem jack (middle and ground lug) together, so with no trem pedal plugged in, the trem is off. I went with cascading gain. I set it up with no parallel mode ( I could change this but no need right now) I kept the normal input jack but, got rid of the bright input jack. I used the hole to mount my gain pot. I kept the 470k (R9 lift one end and then to my gain pot) but I added a 500pf cap in parallel with R9. On the output of my gain pot i changed R8 from 470k to 220k with 100pf cap (in parallel). I got rid of the 10k on V2 input. I like the sound of it a lot. I also added diodes, (two 4001) in paralle with a .001 cap. I ran them from the output of the gain pot to ground. I ran this with a pull pot on my gain pot, to take it in and out of circuit. I know this is not popular but, I love the sound for low volume grind and it kills the volume a little too, for late night playing. The .001 cap gets rid of all the high end fuzz sound. I can get a great clean with the cascading gain, and also a classic rock crunch, very nice. Love this little amp.
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Thanks for the trem info. :smiley: I have managed to do a few mods that I like.
I tied the two lugs of the trem jack (middle and ground lug) together, so with no trem pedal plugged in, the trem is off. I went with cascading gain. I set it up with no parallel mode ( I could change this but no need right now) I kept the normal input jack but, got rid of the bright input jack. I used the hole to mount my gain pot. I kept the 470k (R9 lift one end and then to my gain pot) but I added a 500pf cap in parallel with R9. On the output of my gain pot i changed R8 from 470k to 220k with 100pf cap (in parallel). I got rid of the 10k on V2 input. I like the sound of it a lot. I also added diodes, (two 4001) in paralle with a .001 cap. I ran them from the output of the gain pot to ground. I ran this with a pull pot on my gain pot, to take it in and out of circuit. I know this is not popular but, I love the sound for low volume grind and it kills the volume a little too, for late night playing. The .001 cap gets rid of all the high end fuzz sound. I can get a great clean with the cascading gain, and also a classic rock crunch, very nice. Love this little amp.
Hey Atitagain, Thank you for the tips. I think I'm going to do that for the interim until I get my parallel/cascaded switch going. I'm still messing with the tremolo values. I have them right now at the stock 220k/2.7k values but with 220k for the CF buffer's cathode resistor. I liked the combo of the higher resistor with the 5G9 values and think it might sound simular with a bumping that V2b 220k cathode resistor up to 470k. I'm doing that this weekend and seeing if I like it. If not I'll go back down to those 100k, 1.5k, 220k, 220k values like on my schematic. But I need more dirt out of this amp right now. It's super clean with those V1 tubes paralleled.
What schematic did you go off for your build?
Hey it's funny you mention those diodes. I've been drawing up a parallel/cascaded switchable preamp that I could remotely switch in via relay or the like. I was planning on putting a "fuzz" in it using two diodes like the way you're describing. I was going to setup a push/pull gain pot in one of the vacant input jacks just like you discribe. The way it would work would be only in cathode mode you could pull the pot to select the fuzz. When you stomped on the remote selector you would have a fuzz pedal. The V1b triode acts like a makeup gain stage. If it's not selected you get a normal tube gain boost.
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The diodes for fuzz should sound great. I have some led's (all different colors and sizes) and a bunch of zener diodes ( I think the zener would sound great for fuzz) the two 1n4001 with the .001 sounded best but, there are sp many combinations to try. Off the gain pot it works great because the gain pot adjust how much dirt you get. I was using the marshall 2204 lay out idea for my set up. But I don't use a 10k on the cathode I went with 820 ohms with the 22uf cap. Once I got the voltages of V1 down to 140 volts it crunched out nice and got less stiff. I have the gain pot and volume pot, all with pull switch, I'm thinking of changing the tone pot over to a pull too. The only thing with the pull pots is getting the knobs to fit but having all the options of the pull pots, is worth it IMHO.
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The only thing with the pull pots is getting the knobs to fit but having all the options of the pull pots, is worth it IMHO.
Hey atitagain, I found some knobs that look almost identical to the Ampeg stovetop's but have set screws in them. I'm planning on putting some PEC pots in and some push pull pots all have solid shafts. These should retain the retro look of the amp.
http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=5431550&MPN=1550AG (http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=5431550&MPN=1550AG)
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The only thing with the pull pots is getting the knobs to fit but having all the options of the pull pots, is worth it IMHO.
Hey atitagain, I found some knobs that look almost identical to the Ampeg stovetop's but have set screws in them. I'm planning on putting some PEC pots in and some push pull pots all have solid shafts. These should retain the retro look of the amp.
http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=5431550&MPN=1550AG (http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=5431550&MPN=1550AG)
that's what i was looking for, thanks. I was able to cross reference this knob to the mouser site too (I have an account there) thanks
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Should i change the 220K bias resistors (R33 & R34) to a different value? I think I read some of you saying that 220k is wrong with 6v6's.
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Should i change the 220K bias resistors (R33 & R34) to a different value? I think I read some of you saying that 220k is wrong with 6v6's.
No don't change R32 and R33. Those are the max that you can go. What I was talking about is in the tremolo section R26, R27, R28. In the tremolo section I'm having a tough time deciding if I should go with the 5G9's lower values or the stock J20's. I kind of like the 5G9's but I think it's just because the way the CF buffer is biased. I think if I bump up that resistor with the J20's values for the rest of it it should sound more like the 5G9. I'm looking into dropping that 12DW7 in there and seeing how that performs. I'll have to bump the CF buffer cathode resistor down. I'll start with 47k or so.
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I like the trem but I never heard the fender. The J20's trem is better then my marshall 18 watt. I hear you though, I want to make it better. I have the j20, laying out on the bench, I think I'm done (for now) tweaking it. I have a bassman head that I use for gigs, I have been tweaking that amp for years. Even though I know very little about this stuff, i can't stop tweaking LOL. i wish I could help you with the trem but, I have no idea. Thanks for the info.
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I like the trem but I never heard the fender. The J20's trem is better then my marshall 18 watt. I hear you though, I want to make it better. I have the j20, laying out on the bench, I think I'm done (for now) tweaking it. I have a bassman head that I use for gigs, I have been tweaking that amp for years. Even though I know very little about this stuff, i can't stop tweaking LOL. i wish I could help you with the trem but, I have no idea. Thanks for the info.
Hey I forgot to ask you. You said you cascaded V1a into V1b? Do you still have V2b in the preamp or did you switch that over to use as the CF buffer in the tremolo section?
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I like the trem but I never heard the fender. The J20's trem is better then my marshall 18 watt. I hear you though, I want to make it better. I have the j20, laying out on the bench, I think I'm done (for now) tweaking it. I have a bassman head that I use for gigs, I have been tweaking that amp for years. Even though I know very little about this stuff, i can't stop tweaking LOL. i wish I could help you with the trem but, I have no idea. Thanks for the info.
Hey I forgot to ask you. You said you cascaded V1a into V1b? Do you still have V2b in the preamp or did you switch that over to use as the CF buffer in the tremolo section?
Great question! you read my mind LOL. I was looking at the schematic and trying to see what else I could mess with. I noticed V2b seemed like the last thing before the PI, right? Any way, I was thinking of making it a CF (cathode follower) but wasn't sure if it would work or what it might do? I know in my marshalls I have to use the whole tube and it runs the tone stack (TMB) but the J20 doesn't have that? Would the CF help the trem? Can I wire half the 12ax7 to a CF? To wire 2b to a CF, is it just using pin 3 as the output? You see this is all new ground for me.
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Great question! you read my mind LOL. I was looking at the schematic and trying to see what else I could mess with. I noticed V2b seemed like the last thing before the PI, right? Any way, I was thinking of making it a CF (cathode follower) but wasn't sure if it would work or what it might do? I know in my marshalls I have to use the whole tube and it runs the tone stack (TMB) but the J20 doesn't have that? Would the CF help the trem? Can I wire half the 12ax7 to a CF? To wire 2b to a CF, is it just using pin 3 as the output? You see this is all new ground for me.
I found the tremolo to be thicker with with the addition of the CF buffer in front of the oscillator. I believe it prevents some loading that would attenuate the effect without it. With the addition of the NFB switch to cut the NFB like on the 5G9 Tremolux the effect is really lush. The stock effect is thinner and choppy by comparison. I personally love the effect but I know tremolo is not everyones bag.
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Hey, I need to do a change to that tremolo schematic. If you are doing the tremolo mod you might want to wire it so that you can use a 12DW7 in there to see if you like it. The pinouts are different (just swapped, see the cut sheet). You'll want to wire it so that V2A is using pins 6,7,8 and V2B 1,2,3. Also you'll need to knock that cathode resistor for V2B down to something like 47k (from 220k as shown in my schematic). If you wire it like that you can easily switch between tubes with little modification.
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Honestly, I can't believe you guys are not happy with the stock Tremolo. Mine is so thick right out of the box.
Makes my PR seem like a dud.
I would be interested in more headroom though.
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The tremolo is indeed really good stock, but these mods make that much better. :wink:
I found that I got insane cleans and a bit more volume with the mods above. In fact it had too much clean headroom, I needed to get more dirt out of it. I've been experimenting with cascading V1a and V1b with a gain pot. So far I can get the clean headroom with volume (way more volume :huh:) as before but I can also get smooth hard rock distortion out of it. The way I have it setup it has to be the loudest 20'sumping watt I've ever heard. With the gain pot full and the volume on 2-3 it is like the stock volume at 5-7. But with the gain pot you can pull that down and make it respond like the stock amp so as to not kill yer neighbors. :angel
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What kind of effect did the NFB resistor/cap change bring?
I dont want to remove it completely so I plan to just change out the resistors/cap. I am assuming that change is putting more NFB into the circuit...correct?
The amp is loud enough for me as is. If I need more, I will play my Vibrolux. Just need to get rid of some of the dirt.
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Honestly, I can't believe you guys are not happy with the stock Tremolo. Mine is so thick right out of the box.
Makes my PR seem like a dud.
I would be interested in more headroom though.
The reason for the tremolo change resulted from the opening up of V2b. We changed the the preamp to that of the 18 watt Lite llb, which gave the amp a much better distortion in our opinions. The stock J20 has decent headroom but when it starts to break-up around 6, it sound good but continuing up the dial became flabby, and sore of bee-hive sounding. Changing the preamp to that of the Lite llb gave a much nicer distortion, loss all the bass floppness and bee-hive sound. Also increased the headroom some. This change open-up V2b so hense the tremolo buffer.
IMO, the changes to the NFB resistors also, were for the better. I put mine on a switch, off, the distortion comes on gradually rather then being hit hard. Also the stock feed and shunt resistors made little change switching NFB and Nasty Old Tech came up with old Fender Deluxe black-face values, I believe 820ohm on the feed and 47ohm on he ground, this does make a notice difference in switching for the better.
Anyway, I must agree that the Lite llb preamp makes the distortion much better. I am having a problem with the Lite llb change I can't seem to resolve. I have the same tone as Nasty Old Tech but I lost a bit of wattage or volume with te change that other didn't. I plan on getting it on the bench in the next couple days, always something simple.
I haven't tried the cascade mod yet but just might as the amp has plenty of headroom now and once I find my problem I'll probably have more :grin:
It's not a lot of changes to the J20 preamp to Litellb and you can hang a lot of resistors on the bd. while trying it out, well worth the effort in tone.
The dude(http://)
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I had a friend of mines son pick up one of these it was a floor model.....perhaps a return....I went and tried it out over the weekend ....he didn't notice it was sick , but it is .He was playing at low levels and thought noises were normal.
I will start a different post (Sick j-20) it should be covered under warranty but tech is pretty far away and it may be a simple fix with your help.
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I had a friend of mines son pick up one of these it was a floor model.....perhaps a return....I went and tried it out over the weekend ....he didn't notice it was sick , but it is .He was playing at low levels and thought noises were normal.
I will start a different post (Sick j-20) it should be covered under warranty but tech is pretty far away and it may be a simple fix with your help.
(response to your other post)
I'm arms deep in a J-20 as I write this. There are a few boo-boo design flaws in this amp that need correcting. That standby switch needs to be moved after rectifier you'll see how they wired it (look at the Modifying the Ampeg J-20 thread for the original schematic). That's giving you the bleed in standby.
There's scattered grounding throughout. A good thing to do is to star ground it and divide the preamp's ground from the power amp. Basically everything from the screens back to the transformer tied to its own ground. Preamp on it's own.
The power transformer's lams are paralleled with the output transformers lams causing magnetic coupling. A good thing to do would be to move the PT so that it's bells are facing front and back. I just did that yesterday. Today I've been going through working out all the grounding issues. :sad:
With both the above left stock you'll notice hum, hiss at higher volumes worse with the channels jumpered, and unbearable with them cascaded. Unfortunately I know too well. :laugh:
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While I had the PT out I thought I'd show you guys what looks like something they didn't want you to see. Great place for your "Made In" sticker? :laugh:
(http://i939.photobucket.com/albums/ad240/nastyoldtech/j20pt.jpg)
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While I had the PT out I thought I'd show you guys what looks like something they didn't want you to see. Great place for your "Made In" sticker? :laugh:
(http://i939.photobucket.com/albums/ad240/nastyoldtech/j20pt.jpg)
And it's printed all over the back panel too. I'd like to see an American manufacturer come up with this quality at these prices. Should we all allow the shop-locally ethic to bankrupt us, because last time I checked the people making the huge markup on USA products, really deep down, care about us consumers. I think not.
-MM
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And it's printed all over the back panel too. I'd like to see an American manufacturer come up with this quality at these prices. Should we all allow the shop-locally ethic to bankrupt us, because last time I checked the people making the huge markup on USA products, really deep down, care about us consumers. I think not.
-MM
I'm not knocking the amp. I think it's really well made IMO. I was just poking fun at were they placed their "Made in" sticker as if to hide it. My amp says on the back that it's made in Korea btw.
To comment on your American manufacturing at those prices comment. The J-20 amps were on sale at liquidation prices of $299. Their normal prices were and are up around $850+. Not many companies could stay in business putting out that quality at those liquidation prices. They were just doing a one time blow out their stock on the quick.
I've seen well made American manufactured amps in that +/- ~$1000 with even better quality components and better made for that matter. Heck there are guys on this board that will build you an excellent quality amp for that just ask around.
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I'm not knocking the amp. I think it's really well made IMO. I was just poking fun at were they placed their "Made in" sticker as if to hide it. My amp says on the back that it's made in Korea btw.
To comment on your American manufacturing at those prices comment. The J-20 amps were on sale at liquidation prices of $299. Their normal prices were and are up around $850+. Not many companies could stay in business putting out that quality at those liquidation prices. They were just doing a one time blow out their stock on the quick.
I've seen well made American manufactured amps in that +/- ~$1000 with even better quality components and better made for that matter. Heck there are guys on this board that will build you an excellent quality amp for that just ask around.
Sure I know that. I bought both mine before they went cheep. But even at the original street they are a bargain. I was mainly thinking of the big companies... the American icons if you like. The ones that make us proud then follow up by making us broke. I think Dr Z is making an effort to keep real with prices. I know the amps I build cost around 500 dollars in materials/parts, plus my time, so I realize hand-made up to 1k is excellent I think.
-MM
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Hey everyone, this is my first post. This thread is great. You guys seem to really know this amp.
I've got an Ampeg J20. Overall, its pretty nice. However, distortion/overdrive pedals sound pretty fizzy and fake sounding. The opposite of my 6L6 Blackface amp.
In the J20, I put in new Tungsol 6v6s and 12ax7s, Weber 12F150, and put the NFB on a variable pot. This helped a bit, but not much.
I removed the treble cap from the volume/tone pots and this helped the most. But its still fizzy sounding and now the amp sounds a bit muddy without the cap.
So, does anyone have any good ideas as to how to get rid of the fizz and and balance out the tone of this amp? Any and all info would be much appreciated. I really want to like this amp, but if I can't improve it, I'm going to sell it for a more pedal friendly amp.
I should add, I'm not the most tech savvy with amps, but I do understand some of the basics, can work a soldering gun pretty well, and can follow instructions.
Help! Thanks!
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Okay, no responses....how about this:
Two more questions about the J20:
1. I've read that some people have put 6L6's in their amp. Could I put these in with no other modifications? Could this damage anything?
2. How would putting in different tube rectifiers effect this amp? 5R4, 5Y3?
Thanks for your help!
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I looked at other Fender tremolo amps of the period and found that the 6G16 has that N/S .022uf cap. I figured they must have added that to rid the amp of that same ticking issue. I added it back in and low and behold not only was the ticking gone but the tremolo got really thick and sounded just like those old 50’s recordings with Tweed Tremoloux’s. So good, so good. Maybe one of the best tremolo’s ever put in an amp.
I love that 5G9 trem. Best damn trem in a tube amp. I have a clone I made a few years ago and it is still my favourite gigging amp at the blues club. I had ticking when I first built it, but got rid of that by mucking around with the 'build-out' /slope resistor (1M) in the stock circuit. I can't remember what I changed it to. Biasing it a bit warmer also helps
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1. I've read that some people have put 6L6's in their amp. Could I put these in with no other modifications? Could this damage anything?
6V6s in it now? If so, you can put 6L6s in it, but they would want the bias to be adjusted. The PT and/or OT would be at risk if they are not heavy duty enough.
2. How would putting in different tube rectifiers effect this amp? 5R4, 5Y3?
If there's a 5AR4 in there now, both of those would decrease the B+.
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Solved! I got rid of the fizzzzzzz in the trebles. Thanks to a 100w Weber Ceramic Blue Dog!
I had had a Weber 12F150 in the J20 (sounds amazing in my Blackface)....FIZZ!
Put the Cannabis Rex in the J20 (sounds godly in my Blackface)....FIZZ!
100w Weber Ceramic Blue Dog in the J20....Perfect! I could even put the treble cap back on the amps volume/tone knobs.
I was ready to give up on this amp. Seems its just very picky with speakers. But this Blue Dog and the J20 were made for each other! Nice!
I just thought I would post this to help anyone else that may have the same problem I was having.
Thanks for the help!
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Hi! Could anyone send me the images of the links above?? They aren't in the server anymore... Thank you, that'll be very helpful.
Cheers!
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I have the schematic but it's 325KB too big for here, sent email to me if you want.
al
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Hello!
My first post in this forum...
To heat this old thread up, mods that I have made to my J-20:
The two most important changes: swapped the 12AX7 PI tube for a 12AT7 and speaker for a WGS G12C. The stock speaker is to flabby, lightweight, etc. Maybe a good thing for harp players, who want a lot of crappy distortion from the speaker...
Then I changed the 22µF bypass cap for a 4.7µF to tighten up the bass a little bit, I installed an internal trimpot for bias control also and hooked the C10 bright cap up to a pot, which acts as a presence control. I also snapped the bright cap of the bright channel. When playing with lower volume levels I just turn up the tone-knob a little bit to compensate for the missing bright cap.
I changed V1 and V2 tubes for those expensive TAD 7025 Premium, which was a major improvement, too. Now that amp really shines for rockabilly, r&b, etc. I purchased a TAD extension cab, which is also equipped with a WGS G12C.
Cheers, Chris