New 18W Build

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paniagua
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New 18W Build

Post by paniagua »

First time caller. Recently tuned in. I would like to introduce myself as a lurker and start a build thread where I could hopefully contribute and get some help if needed.

I come from the solid-state Hi-Fi DIY world, however my experience with tubes is very limited. I built an AX84 Hi-Octane for a buddy over a decade ago. Turned out great. Fun project. It still works. Only other tube experiences are recapping and restoring a 300B SET hi-fi amp and building a heaphone amplifier. Found 580V on the 450V rated bulging electrolytics in the 300B and an EZ81 took out a $100 Hammond PT in a 6922/6N1P headphone amp. You'll never guess the blown EZ81 manufacturer :roll: . I'm finally ready to build another tube amp since picking up the guitar again.

I have a few questions before I send off my final component orders...

I was originally planning on building a TMB, or a neutered version like a Trinity S3, but decided to keep it simple with a Lite 2b(ish) with parallel inputs for starters. If i decide otherwise down the road the chassis is already drilled out. My BOM has components for Jason's Mod as well. I want some cleanish headroom for bedroom levels. Otherwise I guess I have an excuse to build a clean amp. My 13yr old plays a lot of higher gain stuff - there's always at least one Metal Zone on the pedalboard.

I already have a chassis and the iron from Mojotone. The chassis has an extra hole for a fuse. I might as well fuse the HT? Does it matter if placed before or after the Standby switch with either an EZ81 or diode rectifier? Would a slo-blo/timed 250mA be appropriate?

I like pedals and have built a few. I want to at least try a passive FX loop for my buffered Boss RV-6, BF-3 and DD-8 pedals. I realize that V1 is biased clean and there may be no benefit. Following the Xtra TMB schematic, right after the coupling cap on the PI's grid, the FX loop is inserted. But I'm not building a TMB. Do I keep the .01uF value per the 2b schematic right after the volume pot and the rest of the FX loop values stay the same as the TMB, including the 68K and 10K in series? Any other values I should pick up to play with? Would this also work as a decent Send into a Roland Jazz Chorus for a Wet/Dry set up? I hope owning a JC doesn't get me banned. I also hope my 18W is quieter and less hissy than the JC :lol:

In addition to a spare NOS JJ EZ81 i won't be using, I also found a pair of JAN Philips 12AX7WA with a date on the box of 6/87 in the my old tube bin. I think I paid $20 a piece for those maybe 15 yrs ago? I looked up what they're going for now and decided I should probably buy something cheaper like a pair of TAD 12AX7 for testing. The Sovtek 12AX7LPS looks interesting as well. I also have a matched Sovtek EL84 and Reflector 6P14P. Any issues with the latter substitution?

Protection diodes going on the not-a-JJ EH EZ81 this time around. I also bought extra UF4007 in case I just want a sand rectifier with a sag resistor. I have 124V coming off the wall. I picked up a bunch of zeners as well.

I really appreciate all the contributors to this community, past and present. I wouldn't be building this amp with you. Thank you. Opinions and suggestions appreciated.
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Re: New 18W Build

Post by JMPGuitars »

Welcome!

From your description, I would take a look at the Superlite TMB before you settle on the Lite. You can build that with SS or Tube rectification, or switchable both. I don't see the point in tube rectification in those circuits though. Tube rectifiers raise the cost of your amp, and reduce the reliability.

I suggest looking at the schematics for a couple different versions of my docs to see how you can implement the FX loop into either of those amps. The FX loop in my docs goes after the cap feeding the grid. It's much clearer in a schematic compared to a layout file.

Thanks,
Josh
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paniagua
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Re: New 18W Build

Post by paniagua »

Thanks!

I was hoping a tube rectifier would be a simple slam dunk to get my rectified voltage in the optimal range without a lot fuss. Since I also have components for SS, I can play around. I have a 10W 150R for the sag with SS rectification as well. What's a good, unloaded voltage to shoot for after rectifier, on the first filter cap, no pre/power amp tubes installed?

If the Lite 2b doesn't have enough gain, the Super Lite TMB would be the next step. I have a 2W October and an efficient 1x12 Cannabis Rex on loan from a buddy to compare with.
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Re: New 18W Build

Post by JMPGuitars »

We generally shoot for 345VDC +/- 5V at point "A" - which is the rectified DC voltage at the first filter cap. That's typically written in the voltage charts.

Your SAG resistor alone won't likely get you there, see my B+ dropping thread in my signature for help with that.

Both the Lite 2b(ish) and the Superlite TMB are excellent amps. You mentioned wanting a TMB and simple build, the Superlite is both. The other thing is that you can get excellent distortion at lower volume with the SL-TMB that you can't with the L2b. They'll sound great either way, and if you want to crank the power tubes for your distortion, you may want an attenuator to keep the volume manageable. YMMV. Whatever you build, I look forward to seeing/hearing the completed amp.

Thanks,
Josh
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Re: New 18W Build

Post by paniagua »

Oh, I see now in the schematic now. I wasn't thinking and reading, assuming there would be a modest V drop at A/first cap with the EL84 inserted and drawing current, and that I needed to shoot higher post redtifier to land at 345V. I want to make sure my first cap V is in the ballpark before connecting PS to rest of circuit and inserting tubes. I loosely followed Paul Ruby's start up method before. I have a Variac.

I'm in no rush. It's not often I get to build an amp. I have teenagers. I hope it takes me 8hrs to wire the heaters :mrgreen: I have a stay-cation in April. Lots of time to sling solder and take breaks playing guitar.
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paniagua
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Re: New 18W Build

Post by paniagua »

I'm finalizing layout, following and borrowing from other 18W variations. I come from the hi-fi world and worried about noise. The OT secondaries will be running underneath but parallel to the diodes above on the board. Will there will be any coupling issues with the diode rectifier currents and the OT secondaries as shown in the picture? How sensitive are OTs to picking up noise? I have space to tuck the rectifying loop elsewhere with terminal strips, but I figured I would try to squeeze it on the board since I have the extra length.

The G10 epoxy board will be mounted on 3/4-7/8" stand-offs - I have a mix of 1/2" and 3/8" stand-offs. The 2 smaller black dots are the mounting holes for the board and the larger black donuts represent the chassis hole cut-outs for the OT windings that exist under the board.

I'm following the well established 18W grounding and input schemes to the letter.

Screenshot from 2023-04-04 13-49-44.png
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Re: New 18W Build

Post by JMPGuitars »

To answer your first question, you are correct; the unloaded voltage will be much higher than the loaded voltage. The 345VDC target is with ALL tubes installed in the circuit.

The second question, about layout, lots of people do similar things. The main thing you want is to consider if any wires will need to be shifted during troubleshooting/noise reduction stages of the build. You want your leads to be as short as possible, but still have enough slack in case they need to shift.

Personally, I like to have the SS rectifier diodes go directly from the PT to the standby switch. I don't see a point in wasting circuit board real estate for those diodes.

Thanks,
Josh
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Re: New 18W Build

Post by paniagua »

Thanks Josh. I have more than enough space to mount the diodes elsewhere. I already bought an EZ81. I just mounted some turrets with the tube socket to easily convert to SS if the new production EZ81 I have gives me trouble. I just need to start building and stop worrying and planning. :mrgreen:
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Re: New 18W Build

Post by JMPGuitars »

paniagua wrote:
Sat 04/08/23 9:11 am
Thanks Josh. I have more than enough space to mount the diodes elsewhere. I already bought an EZ81. I just mounted some turrets with the tube socket to easily convert to SS if the new production EZ81 I have gives me trouble. I just need to start building and stop worrying and planning. :mrgreen:
If you want to run both rectifiers and be able to switch between them, check out my layout for the Xtra TMB series: files/JMPGuitars_18W_Xtra_TMB_Layout.pdf
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Re: New 18W Build

Post by paniagua »

18W_Initial_Voltages.jpg

Phase 1 of build went fine without drama. Just need to order head cab and design face plate. I went with 2b(ish) with Hi/Lo inputs.

Voltages are high, B+=369V, even with an EZ81. Protection diodes in place. I'm assuming the EZ81 is working. Maybe I should pull it and measure with just the protection diodes in place? I'm at 100.8% plate dissipation with 123V coming off the wall and 13.3V on the cathode, assuming 12W per plate. I'm kind of surprised. I assumed that since Mojotone uses these TXs in their kit my voltages would be lower.

I'm using matched 6P14P. Bought them from The Tube Store. One appears to be a bit more microphonic than the other. I have an old matched pair of Sovtek EL84 lying around. Should I expect the 6P14P to draw more current than a standard EL84?

I guess I need to knock down the voltage a bit. I know the 6P14P are rated 14W but with a 103dB sensitive Cannabis Rex, there's too much head room. I have a bunch of zeners and a terminal strip already mounted to place to string them in place right after the EZ81. Less efficient right after the rectifier, but a couple 20V or 15V zeners should get me in the ballpark? I also have 200R and 220R cathode resistors. I have a 150R sag resistor on hand but that will only drop around 10V. I also have a CL-90 on hand but I doubt that it will drop the primary V that much.

I'm going to play the amp for a few days before I can get around to dropping the voltage. Right now, I'm kind of blown away by how amazing this amp sounds. It just sounds a little "stiff". I want some headroom, but this is maybe a little too much. There's a little hair on the Hi input and with my humbuckers turned up, but I have to really crank it to get any sort of mild compression or OD. I have a friend bringing over a less sensitive Eminence Legend for me to try.

Also, amp appears to be quiet. Dead quiet with inputs shorted other than a very very low level, like your ear a few inches away from the speaker soft hum. Not a buzz or ground loop. Maybe heater/cathode. It completely disappears or gets buried once I plug a guitar in. Hiss, way way quieter than my Roland Jazz Chorus. 8) Like not even close. I'll post some pics when I open the amp again this weekend.

Thanks!
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Re: New 18W Build

Post by JMPGuitars »

Nice, congrats, it sounds like you're well on your way to an awesome amp.

For all the things you described, get your voltage where you want it before you worry about anything else.

It's not always the same, but IME, if you place the Zeners before the 1st filter cap, then they'll drop around half their rated voltage. I would place 40 to 50V worth of 5W or higher Zener diodes in line and see how your voltages look, and see how the amp sounds before you do anything else.

Getting your power tubes to around 85% should also get you to the land of happy noise.

Also note that the pin 2 voltage on V3 is too high (V4 looks better). This suggests that you may need to clean up the soldering on the path to ground from there.
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Re: New 18W Build

Post by chaliapin »

I would try the other tubes and check the pin 2 grid voltage.
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paniagua
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Re: New 18W Build

Post by paniagua »

Thanks for all the help guys.

Yes, I thought about swapping the same tubes around to see if abnormal pin2 voltage moved to V4 position. The abnormal pin2 was on the microphonic tube in V3. I went a little light on the solder but my joints looked perfect otherwise. I ohmed out again and everything looked fine. I reflowed a few joints and now getting identical, 0.02V on both pin2 of V3 and V4. Go figure.

Going to add 20V x 2 zeners tonight.

My 13yr old was blown away with the amp. Slapped a Boss RV-6 and DS-1 pedal in front last night and had a blast. The differences between the reverb types are much much more apparent with the 18W compared to the JC-40. No comparison.
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Re: New 18W Build

Post by paniagua »

PXL_20230427_104922964.jpg
20V x2 zeners placed after rectifier. I have no idea why my V dropped on pin3 to 347. Shouldn't that have remained the same 370V I was reading before and the zeners should have dropped V to 350V? You can see that each zener dropped about 10V a piece. No changes made to socket other than soldering new wire length from pin3 to zeners. The B+ is fuses right after the zeners before going to the cap can. The EZ81 is brand new, Electro Harmonix. Same results with a different JJ EZ81. TX doesn't get terribly warm.

I removed the EZ81 when soldering the zeners. Maybe it just needed to be reseated or a flakey Belton pin contact?

Like I said before, one of the 6P14P was microphonic. I ended up swapping in some Sovteks. Similar readings as above with either set in. Also, I take initial readings after B+ applied but wait 30min before taking final readings.

Thanks!
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Re: New 18W Build

Post by JMPGuitars »

Post some high res photos of your build so we can see what you've got going on.
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Re: New 18W Build

Post by paniagua »

Not sure if the dynamic interaction between the V drop across the zeners and the effect on the bias affects the efficiency and/or current across the zener and/or EZ81 drop? Replaced one of the 20V zeners with a 5.1V. Right now, getting 12V drop (5.1V + 20V zeners), showing approx 50% drop. Initial B+ was 365V before I placed the zeners this time. B+ now sitting at 345V and EL84 cathodes at 12.6V. All other voltages look perfect. Also, is the EZ81 just glorified resistor since the protection diodes are doing the actual rectification - would this affect the V drop across the EZ81? Everything sounds and looks to be working fine. Happy.

I would call this a quiet build. Self-noise on par with my Boss Katana 50 on 25W output setting. I do have filthy mains though. Our refirgerator pumps junk and hum. The microwave is on a separate dedicated breaker and I can hear it through the amp. Pedal board adds some hiss with all pedals off but it's really only noticable when the volume is above 9 o'clock. With 103dB sensitive speakers, that's really loud in my house.

Not sure how much value there is in an FX loop in the 18W design but I wanted to find out. I went ahead and installed and uninstalled the passive loop today. Major ground loop hum, with and without pedals. I tried a couple different groundings and couldn't get rid of it. Might want to revisit it later, but I'm happy with my delay and reverb in front right now - I just want to play guitar. I was surprised by how different the different modes on each pedal sound so different from one another. Before the differrence between Tape and Warm delays was subtle. Now I have to turn the effect level/mix down.

I have a freind bringing over a 100dB cab this weekend, hoping to reduce headroom just a bit. Had more time to play with my dirt pedals today. They sound much better through tubes.

This amp sounds super dynamic and very responsive to picking strength. I was hoping it would be this good.
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Re: New 18W Build

Post by JMPGuitars »

Sounds like you had a gremlin, and got rid of it when you changed your Zener situation. Nice.

Play around with the touch sensitivity while you're having fun. Finger pick gently with the gain up half way, then smash a chord.
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Re: New 18W Build

Post by colossal »

Very nice build.

I noticed in your photo that your power tube cathodes are not linked, or if they are, then the connection is made under the board and not visible.

I would rewire, like this:
18W.jpg
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Re: New 18W Build

Post by Bieworm »

colossal wrote:
Thu 05/11/23 7:33 am
Very nice build.

I noticed in your photo that your power tube cathodes are not linked, or if they are, then the connection is made under the board and not visible.

I would rewire, like this:

18W.jpg
Good point , but there are more underboard wires ..so it’s likely the cathodes are connected there. The voltage chart doesn’t show the obvious discrepancy neither imho
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Re: New 18W Build

Post by paniagua »

Thanks. Yes, mix of above and below board connections. EL84 cathodes are linked.

A friend brought over a smaller cab loaded with a 10" Eminence rated at 100dB. We were both surprised by the difference in volume level and the earlier break-up achieved compared to the 103dB Cannabis Rex. I found a well broken in cheap Celestion Seventy 80/8ohm 98db locally for $35. If I don't like it, it can serve duty as a bench test speaker and probably just buy a Greenback if I want more earlier break-up.

When we cranked the 10", I blew the replacement Reflector 6N14P. Was working fine before. It appeared to be red plating and developed high level of hum. I decided to cut my losses with these tubes, got a refund, and picked up a set of TAD EL84. No complaints. I like them a little better than the Sovteks. Took some measurements and appear to be well matched and quiet so far. I found an old Sovtek 12ax7LPS in the tube bin I might try in the PI. I also have some JAN 12ax7WA I haven't rolled yet.

I ordered the head cab and should hopefully be here in a couple of weeks. I'm holding off on the faceplate, thinking I might want to add something more than volume and tone, but I'm struggling to justify more. I'd like a little more edge of break-up at sane volumes but a speaker change could fix that. I have 120K resistors I could swap on the plates. I could just build an attenuator as well. But there's already a world of tones in just the amp vol/tone knobs, and especially the guitar vol/tone knobs. I was surprised how well the amp responds to the guitar controls. I haven't even bothered to put my Boss EQ-200 on the pedalboard.

My boy has been spending more time playing guitar since building an 18watt. He plays in the dark sometimes, just to stare at the tube glow. He's impressed. We spent a lot of time together talking about and building the amp. It's been cool to hear him experimenting more musically, trying new songs, and messing around with pedals. He nailed a Ritchie Blackmore tone the other night. Cool. Priceless proud dad moment.
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