new TRT 100 findings [message #8083] |
Mon, 22 January 2007 07:27 |
stevem
Messages: 4772 Registered: June 2004 Location: NY
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Over the weekend I lent my 2001 TRT 100 all tube Kustom to afriend to gig with while I repaired his amp, and when I got it back on sunday I had time to really run it thru its paces and address some things about it I wanted to improve.I picked this head up when the muscians friend folks where blowing them out for 400 bucks, down form their original price of over 700 bucks, and now I know why!
The amp is made ok, or as you would expect for something made in china, but it does have some strong points.
It has nice semi torodal power and output transfromers, a full size reverb pan, and in their USA done design Kustom kept all the potential A/C preamp hum causing wiring on the back wall of the amp with all the preamp section on the front wall.they also have a nice vented steel cover on the back to protect the phase inverter and the 4 output tubes and its these 6l6gc output tubes that where part of the mystery I came across.
Since I got the amp I have only used it 4 times for rehearsal, and I never liked the lead channel as for me I needed more highs then it could give, and also the amp did not sound like it was putting out 100 watts rms thru its 4-12 cabinet, and as it turned out I was right.
In testing it out on sunday I found it to be out putting only 62 watts RMS, a far cry from 100.So I did some more test at different impeadance loads to see if the output trnasformers secondary wires where hook up right, as I have come across this problem with many tube amps before, but they where right.Then I checked out the schematic and noticed that the output tube sockets where wire with pins 1 and 8 being common and I also noticed a location by the output tube bias adj pot where a resistor was left out and that really made me wonder and pull my beard.
So I grabed my marshall and yanked out its four EL34 output tubes, stuff them in the Kustom and reset the bias and fired it up.Sure enough the amp then put out 84 watts RMS. The only thing that may be a problem with this change is that the EL34s unlike the original 6L6GC tubes need more heater current as the voltage with the 6l6s was 6.1 and it dropped to 5.8 volts with the el34s so I need to run a long test a see just how hot the power transformer may get do to the extra load. If worse comes to worse I can install a seperate filiment transformer just for the output tubes.
I do not know what the story may be with the TRT100s litle brother the TRT50, maybe they got the output transformer right in that model for its 6L6GC output tubes, it would be interesting to find out, but know I know one of the resons why they never sold that well and had to blow them out at that 400 price, you`ve got a amp advertised as being 100 watts rms wimpin out a 60 watts rms due to its mismatched output tubes and output transformer!
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Re: new TRT 100 findings [message #8125 is a reply to message #8083] |
Mon, 29 January 2007 16:41 |
daveobergoenner@gmail.com
Messages: 104 Registered: January 2007 Location: Missouri
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Steve:
As best I recall, the best plate to plate impedance for a pair of 6L6's around 6600 ohms. For a pair of EL34's more like 4300 ohms.
Half of that for a quad of each...or 3300, and 2150.
You could pull the output tubes, and measure the output transformer backwards to figure out what it's primary impedance really should be. Watch out however...just a few volts into the secondary will produce a lot of volts on the primary.
The EL34's should last a long time with only 5.8 volts on the fil. Have you checked to see how much current they are drawing? I guess if the plates aren't starting turning red, they are probably OK.
Dave O.
Dave 0 Wall-O-Bass
Webpage - <a href="http://webpages.charter.net/daveobieone/" target="_blank">http://webpages.charter.net/daveobieone/</a >
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Re: new TRT 100 findings [message #8126 is a reply to message #8125] |
Mon, 29 January 2007 16:43 |
daveobergoenner@gmail.com
Messages: 104 Registered: January 2007 Location: Missouri
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Senior Member |
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BTW, did the sound of the amp improve with the EL34's?
Dave O.
Dave 0 Wall-O-Bass
Webpage - <a href="http://webpages.charter.net/daveobieone/" target="_blank">http://webpages.charter.net/daveobieone/</a >
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Re: new TRT 100 findings [message #8138 is a reply to message #8132] |
Tue, 30 January 2007 09:52 |
daveobergoenner@gmail.com
Messages: 104 Registered: January 2007 Location: Missouri
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Senior Member |
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I'm really interested in this amp...
Seems like 45ma should still be OK for the EL34's. At 500 volts, that gives idle power of 22.5 watts, which is below their 25 watt rating.
I'd love to see a few pix of the insides of this thing...If you could snap a few next time you have it open. If there's space, an additional filament transformer would be a very good idea. I'd look for one with metal end-bells, to reduce the hum.
Torroid output transformer cores are also (generally) fairly intollerant of unbalanced current to the output tubes.
I'm guessing it does not use an ultra-linear output configuration? Fender tried using that in some of their tube amps about 20 years ago, and it was not well received by guitarists. Works great for Hi-Fi, and might be OK for bass, but not what you want for guitar.
Thanks,
Dave O.
Dave 0 Wall-O-Bass
Webpage - <a href="http://webpages.charter.net/daveobieone/" target="_blank">http://webpages.charter.net/daveobieone/</a >
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Re: new TRT 100 findings [message #8140 is a reply to message #8083] |
Tue, 30 January 2007 13:20 |
stevem
Messages: 4772 Registered: June 2004 Location: NY
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Yea I would be ok with 45ma too but in this amp the outputs start to add their grind just a tad to early.Their is also plenty of room for a suplimental filiment transformer, the amps output and power transformer are only simi torridal not fully toridal and the output stage in not ulralinear like my fender 1976 proreverb which has a interesting story about its output stage that may point a clue at why they sounded so bad.After having this amp for some years I got some nice RCA black plate 6l6s to stuff in it and ditch the sovtecs that it had, so after putting the new ones in I hooked the amp up to my load resistor and scope to see what it would put out wattage wise hoping for a improvment as it never sounded like a 70 watt RMS amp to me from day one, and my 42 watt bandmaster would give I a good run for its money any day.Well I fire it up to test it and its putting out all of 48 watts, and after a while I find out its got a twin reverb output transformer in it, and I always wondered since I got the amp why the output transformer was so large for a 70 watt amp, well now I knew why!
This transformer is original to the amp, its plate leads have never been unsoldered from day one, they look like when the amp left the factory, so its my guess that alot of these proreverbs where made this way due to the fact that the twins where made on the same chassie so at the factory their must have been some mess up where some proreverbs got the twins output transformer.
So anyway what it did with mine was rewire the 2 8 ohm drivers to serise to get the impeadance load right and I got my 65 watt RMS amp,I guess fender was hopefull back then that the amp would do the output numbers the math crunching said it would.
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Re: new TRT 100 findings [message #16847 is a reply to message #16846] |
Wed, 28 March 2012 15:14 |
Kustom_Bart
Messages: 601 Registered: October 2010 Location: Greenville, MichiGUN
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You should be good then,
25 div by 480v = .052 or 52ma x .7 = 36.4 bias
so 38 is fine you could go 40 and it would break up a little easier. 31-32 would be slightly under bias to make it really warm nice cleans.
38 is a great bias setting.
The one thing that you want to remember at least this was told to me by Bob Rissi www.rissonamplifiers.com this guy knows his stuff. He told me that EL34's and 6550 tubes are the most efficient tubes and you can push the bias a little bit on them and get a good clean tone still. He said that these should be the tubes of choice whenever you change tubes if you can change to them, do so. I know I love EL34's and I have a Risson amp with 4 6550's in it that just screams at 240watts.......
[Updated on: Wed, 28 March 2012 19:23] Report message to a moderator
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Re: new TRT 100 findings [message #16848 is a reply to message #8083] |
Wed, 28 March 2012 20:56 |
stevem
Messages: 4772 Registered: June 2004 Location: NY
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Senior Member |
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That statement by Bob is not fully true, as the two tubes he speaks of are quite different, and not just for their power output!
A 6550 along with a 5881,6L6, 6V6,7027a,8417,7581a, 6CA7(EL34s brother) and some 3 or 4 other tubes, all have beam forming plates as part of there structure, and as such pull current and hence power much faster than a EL34 or EL84 for that matter!
These two latter mentioned tubes are more dynamic when played and listened to closly, in other words they have more range between being clean and then going into clipping when set up right, and even more so in a amp circuit that imploys no negitve feed back from the output stage!
A nice combo I find to utilize in somewhere around a 70 watt amp with 4 output tubes is to run two 34s and two JJ 6V6s, but you need to have a split bias system in place, but atleast the JJs can live with 500 volts on the plates if need be!
[Updated on: Wed, 28 March 2012 20:57] Report message to a moderator
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Re: new TRT 100 findings [message #16870 is a reply to message #8083] |
Mon, 02 April 2012 06:51 |
stevem
Messages: 4772 Registered: June 2004 Location: NY
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Senior Member |
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Yea, you pay alot of money for those russain made tubes due to the purchase of the gold lion name!
The Groovetubes version is a Chineess made one to groovetubes specs and has been very reliable.
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