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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Wed Apr 17, 2013 8:06 pm
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I am very happy to report that I think I have succeded in taming the beast.

I decided to reinstall the 68k grid input resistor on V1 (the TW Express does not use one), but this time instead of installing it on the eyelet board as in the JAVA layout, I soldered it directly to pin 2 of V1. To make it easy, I soldered the loose end of the resistor into an eyelet hole at the edge of the board and ran the shielded cable from the input jack to that point. With this change, the noise (both hum and hiss) dropped dramatically.

I also rerouted the wires connecting the bright switch to the volume pot. The input wire runs directly from the pot to the switch and the wire from the caps runs to the eyelet hole for the wire that runs back to the center wiper of the pot. Things are now separated to the max. The caps no longer seem to break into oscillation due to the wires being too close together.

I also ran a ground wire from the back of the presence pot to a ground lug (one of the power tranny's studs). The pot no longer cuts out at max clockwise.

Finally, I went back to a 10k tail resistor (from the JAVA 22k) and upped the feedback resistor from 47k back to 56k for a slight increase in loop gain. I doubt I will go back up to the 100k feedback resistor as the amp has plenty of gain with the 56k.

The amp is fairly bright. So much so that the 100 pf bright cap is not really needed. I may just go with the SPDT switch and a single 50 pf cap which gives a nice boost with minimal noise. The treble control is no longer distorting the signal at max clockwise either. Amazingly, as bright as the amp can get, it is not ice picky at all. It has a very smooth treble response.

Flipping the gain switch to cut out the V1 cathode bypass cap gives a nice bluesy clean tone.

With the amp volume at about 9:00, turning up the volume on a humbucker equipped guitar goes from a nice clean tone to just starting to break up with the guitar volume on 10. Turning the amp volume up to about 11:00 gets the same effect with a Strat.

Hiss is pretty low in level until the amp volume is turned up to about 1:00, then it starts to get a little louder. I haven't had the nerve to play the amp at that level yet.

The only problem that still occurs occasionally is the hum and hiss that happens when the amp is first turned on, but quickly dies down. I'm not hearing any crackles either anymore.

I biased the amp at about 34 mA plate current and 480 VDC plate voltage for about 60% max plate dissipation (25 watt E34Ls). The amp is really sounding good and I can't wait to crank it.

I'll post more photos of the final wiring layout when I pull the amp out tomorrow, also some finished shots in the cabinet when my name plates arrive. Until tomorrow. :D

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Apr 18, 2013 1:39 pm
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Outstanding job Bill!! 8)

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Thu Apr 18, 2013 10:01 pm
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Just when you thought it was safe to go back in the water .... something comes up and bites you in the butt.

Last night I thought that the problems with the presence pot were solved. They weren't. They were just masked. I discovered tonight that as the overall volume was increased, the amount that the presence pot could be turned up decreased. With the volume at 9:00. I could turn the presence up all the way. With the volume at 11:00, the presence pot would start to act flakey (breaking up and hissing) at about 4:00. By the time the volume was at 12:00 noon, the presence was dropping out. Beyond 12:00 noon on the volume control, the amp would break into oscillation. WTF?

Ok, I figured the loop gain was too high (PI tail was 10K and feedback resistor was 56K, where I left things last night). I tried different combinations of PI tail resistor and feedback resistor going from less feedback to more feedback. I finally ended up at the stock JAVA configuration with a 22K PI tail and 47K feedback resistor connected to the 16 ohm tap of the outout transformer. The amp still began oscillating as the volume was turned to max.

I was stumped and frustrated. I finally decided that I had to take drastic action and removed the presence pot all together. I decided that the amp was bright enough and between the range of the treble control and the bright switch, I could live without the presence pot. So there is now a big empty space where the pot used to live.

Image

I then played with the PI tail values and feedback resistor. Long story short, I found that the amp would break into oscillation when the loop gain was greater than about 56% of the open loop gain. I could find no reason for that to be true, other then component location and lead dress. I couldn't change location of the parts and I had redressed the wires multiple times already. I finally ended up with a PI tail resistor of 10K and feedback resistor of 56K. Right back where I was last night. But I can now crank the volume to max (not that any sane person would want to without hearing protection) without the amp breaking into oscillation. There is still plenty of gain for the amp to overdrive fairly easily.

This photo shows the 4.7K resistor that replaces the presence pot connecting between the PI tail and ground. The photo also shows the routing of the bright switch wires and the shielded input cable.
Note that the photo was taken before the 22K tail resistor was replaced with the 10K.

Image

Finally, here is a photo of the grid resistor on V1 and the other end of the shielded cable.

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As of tonight, the amp is very quiet (up until about 1:00 and then the hiss starts getting noticably louder). If everything continues to work like this tomorrow, I will declare victory and bolt the amp into the cabinet. I'll also post photos of the completed amp. Once I am more mobile, I'll post sound clips. The amp really does sound nice when it is working properly. :D

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Fri Apr 19, 2013 1:50 am
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An amazing thread. The agony and the ecstasy. Hopefully. :D

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Fri Apr 19, 2013 8:05 pm
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Congrats Bill! I knew you would figure it out, but sounds like this one did test ya a bit! Looking forward to seeing the completed amp and some sound clips when you put that walker away. These builds make me want to try one myself, but after seeing the amount of difficulties you had with all your experience I might just stick to refurbing vintage amps instead!

T2

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Fri Apr 19, 2013 10:10 pm
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Well, she is finished. :mrgreen:

And the amp is a "she" as you will see shortly. :wink:

When I fired her up today, I found a few pesky problems still plauging the amp, mostly in the form of snap, crackles, and pops. I was also still having some problems with oscillation at full volume.

However, I still had one mod to do, which I decided to do first in case it caused more problems, so I could trouble shoot things only once (famous last words :lol: ). I had decided to replace the two cap bright switch with a single 100 pf cap switch to cut down on wiring and parts. I ended up replacing the two Radio Shack switches (DPDT and SPDT) with two Carling SPDT switches. The bright switch is on the bottom (you can see the cap peeking out from behind it) with the gain switch above.

Image

Next, I discovered that jiggling the input plug was causing crackles and pops. In fact, just the weight of the plug was causing random crackles. So, I made sure that all the solder joints were good, bent the tip prong to make better contact with the plug tip (I did the same with the speaker jack tip prongs) as well as bending the shorting prong to make good contact with the tip prong with no plug inserted. After all that, there was still some slight crackles with the plug inserted, so even though the jack was grounded through the barrel to the brass plate, I decided to ground the jack to one of the circuit grounds. Bingo! Big drop in noise.

Image

Finally, just to be sure, I ran a ground wire from the brass plate to one of the power transformer studs. Result? The crackles and pops are gone! :D

Image

One final test of the amp showed that other then a brief hum that quickly disappears when the amp is first switched on, she is extremely quiet. The hiss remains low until about 12:00 noon, then at about 1:00 it begins to get louder. With the volume maxed out, the hiss is quite loud but the amp when played is even louder. In fact, for the few brief notes I hit, I would say this 35 watt amp is even louder than either my 5F6A clone or BDRI (both low gain, 40 watt amps with 6L6GCs). Obviously the four 12" speakers have a lot to do with that but the amp is like WOW!

So now, finally, it was time to install the amp in the cabinet. The first order of business was to line the bottom of the cab with aluminum tape to help shield the amp guts.

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Next was the obligatory tube chart.

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Something new: my chicken scratch signature.

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The amp finally bolted into the cab.

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Back panel installed.

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Close up of the model plate. Most cloners of the TW Express name their amps some variation of "Train Wreck" or "Express". I decided to call my amp the "Wrecking Ball". Also, Ken Fischer did not give his amps serial numbers, instead giving them female names. I decided to do both, naming the amp after my wife, Debbie, and the serial number being the month and year of the amp's completion followed by the amp number. I assured my wife that there was no relation between the model name and her name. :lol: :lol: :lol:

Image

Here we see the front of the amp.

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The completed half stack. When I get some more money, I'll probably get some better speakers for the cab and have a "BlueSky Amps" nameplate made for the front grille.

Image

Finally, the completed half stack with my Strat.

Image

First impressions: This amp is loud! The cleans are very nice, but very different from either my 5F6A clone or BDRI. The highs are smooth with no harshness, even with the bright switch on with the Strat bridge pickup. Haven't tried my Tele through the amp yet, though. The breakup starts to occur between 9:00 and 11:00 depending on if you are using humbuckers or single coils.Overall, the amp is very sweet sounding. I am very pleased. :D

Next up: lessons learned on building a high gain amp.

To quote the Grateful Dead, "What a long, strange trip it's been".

See ya next time. 8)

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sat Apr 20, 2013 5:44 am
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Bill...She looks fantastic :!: :!: And I like the way you worked around spending so much time with her by naming it after your wife...You are a GENIOUS :!: This won't even cost you a pair of shoes :lol: :lol: :lol:

Again great looking amp, and another quality build by BlueSkye Amps...Thanks.

T2

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sat Apr 20, 2013 8:30 am
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Thanks, T2. My wife was very touched. :D

This morning was cleanup time. Neatening up my work bench, vacuuming all the little bits of wire off the floor, digging solder splatter out of the ceiling (J/K :lol: ), etc. before trying the new girl out.

I thought I would include a shot of my work bench. On the bench with the towel are general tools and cleaners, polishing cloths, etc. On the other bench are my tool kits, DMMs, O-scope, and printer. Hidden in the back are my signal generator and dummy load. Fortunately, I did not need the O-scope or sig gen, but the dummy load came in handy when biasing the amp.

Image

Finally, here is an overall shot of my little amp collection. From left to right: Frontman 25R with Ragin Cajun 10" speaker, 5F1 configured Champion 600 reissue on top of a Raven 1x12 cab with a Celestion G12P-80 8 ohm speaker, Wrecking Ball "Debbie" on top of a Crate 4x12 cab, 5F6A clone, and heavily modified BDRI with 12" Cannibis Rex speaker. In the cubby hole below the tweeds, you can see my little pedal board and all the sheet music books I can't play. :lol: :lol: :lol: :lol:

Image

Ok. Enough typing. Deb is walking the Girls. Time to fire the other Debbie up for a few minutes. :D

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Last edited by bluesky636 on Mon Apr 29, 2013 3:56 pm, edited 1 time in total.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sat Apr 20, 2013 10:34 pm
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Been playing the Wrecking Ball off and on today in between getting my hair cut, going out to lunch with my wife, and running errands (she is still driving), comparing the new amp with my Strat to my 5F6A clone and in the process, discovering something interesting about the amp.

As I mentioned previously, the amp is quite bright but not at all harsh sounding. It makes my 5F6A sound very dark, but is an interesting contrast. Tomorrow I'm going to compare her to my BDRI with a humbucking guitar .

Anyway, having a solidstate rectifier, I was concerned with the high B+. Currently the amp is biased at about 33 mA plate current and 482 VDC plate voltage. A little research found that a true Trainwreck B+ runs closer to 400 VDC. So I took a look on the Weber site and found a zener diode kit that they sell for dropping the B+ by either 20, 30, or 40 VDC.

https://taweber.powweb.com/store/vdump.htm

After a few calculations showed that the 30 VDC version would give me a reasonable B+ with the capability of slightly higher plate current, I placed my order. Not sure where I am going to mount it as the circuit side of the chassis is pretty crowded, but I might be able to mount it on the top side of the chassis. I also decided to add a thermistor to the primary side of the power tranny to slow the in-rush current a bit. A thermister is also recommended to be used with the diode so I ordered three of them (one as a spare).

While investigating the high B+, I noticed that my power tranny configuration was a little different than that shown in the schematic and wiring diagrams. My tranny was lacking the 125 VAC primary side input (having only the 120 VAC input) and was also lacking the slightly lower voltage secondary output. The part number looked correct. But then I noticed that the prefix of the part number of both my trannys was different than that shown. A quick check of the Weber website revealed that the power and output trannys were both actually Heyboer transformers vs the no-name (and probably Chinese made) trannys that were supposed to come with my amp! The two Heyboers were a $20 option for the kit that I did not order. Pretty interesting. I do know that PRS uses Heyboers in a few of their custom amps, so the trannys must be pretty good. :D

It should be interesting to see (and hear) if the thermister and lower B+ make a difference in tone (I know the bias will be affected). Not sure when the parts will arrive.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Sun Apr 21, 2013 9:24 pm
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I tried the Wrecking Ball with both a humbucker equipped guitar and my AVRI 52 Tele. The humbuckers really drive the amp into a nice distortion. I also have to turn the bass control almost all the way down with humbuckers because the bass output is so strong.

The Tele sounded really nice through the amp. The pickups are not hot enough to overdrive the amp at the same settings as the humbuckers, but the cleans are really nice. Even the Tele bridge pickup sounds very sweet through the amp given the smooth highs that the amp exhibits.

So far I have played four of my six guitars through the amp and other than making minor adjustments to the tone and volume controls, all of the guitars have sounded really nice.

I need to buy a new power conditioner as I am out of outlets on my old one. I have the Wrecking Ball plugged directly into the wall outlet and while my wife was vacuuming downstairs, I could hear the electrical noise on the line through the amp but not through my 5F6A clone which is plugged into my power conditioner. I'm looking at getting this conditioner from Sweetwater:

http://www.sweetwater.com/store/detail/PL8C/

It has two isolated banks of four outlets each which would allow me to plug in the pairs of amps I use togther most often into separate banks for best noise filtering and isolation. Only problem is, I need to change my account password and I can't remember the answer to my secret security question. Heck, I didn't even know I had a secret security question. :lol: :lol: :lol:

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 22, 2013 4:55 pm
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Great build and great thread, Bill. Thanks for inviting us all along for the trip.

Now, remember, not too much of the Johnny Walker while using the walker. :lol:

Art


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Mon Apr 22, 2013 9:57 pm
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Art1 wrote:
Great build and great thread, Bill. Thanks for inviting us all along for the trip.

Now, remember, not too much of the Johnny Walker while using the walker. :lol:

Art


Thanks.

It's not over yet. Now that I have solved the noise problems, I'm going to revisit the feedback resistor and presence control. I think the main problem was a grounding issue and that appears to be solved. Gonna try shielded cable to connect things. Stay tuned. :D

PS: I favor Glenfiddich or Glenmorangie myself. :mrgreen:

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 23, 2013 2:12 am
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Bill I did not read all the post but if you still have noise in your amp you may need to use shielded wire from volume pot and ( if needed) every signal path going to 12XX7 input grids.

As you know , non- shielded wire going to input grids could act like antenna .Same with resistor or capacitor with long leg.

Nice looking amp , you do nice job.


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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 23, 2013 6:12 am
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stratele52 wrote:
Bill I did not read all the post but if you still have noise in your amp you may need to use shielded wire from volume pot and ( if needed) every signal path going to 12XX7 input grids.

As you know , non- shielded wire going to input grids could act like antenna .Same with resistor or capacitor with long leg.

Nice looking amp , you do nice job.


Thanks.

Yes, I used a shielded cable. Its all covered in gory detail in the thread.

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Post subject: Re: New Amp Build - Trainwreck Express Clone
Posted: Tue Apr 23, 2013 6:49 am
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bluesky636 wrote:


Yes, I used a shielded cable. Its all covered in gory detail in the thread.



I did not see them on photos , just at the jack input. Probably "first " version of the amp ?


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