Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bigdaddy on June 18, 2010, 06:56:59 pm
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I took a 6K6GT and put it in one of my BF type champs. It has an Allen TP-18 and T0-8C transformers. The TP-18 is a nice tranny that will give you 340VDC. So it was great for the 6K6GT. Speaker is a Weber 8" 4 ohm CVC. I had to change the bias resistor to 1K from 470R. It actually sounds better, originally it had a Brimar 6V6GTY. I'm very excited about the 6K6GT power tube, it's tone is nice and breaks up the way I like with rich harmonics. I'm getting 8watts at 320V from my bias meter.
Anyway the amp is not very loud but has a wonderful tone and quality to it. Still a little too loud but when I get the isolation area it should work out just fine. I plan on building the firefly also and have the Killer Ant coming Monday, plus the Weber mini mass attenuator. But this is a great replacement for the 6V6 providing I can get the voltage correct on some other amps.
I was wondering if there were other tubes similar to the 6K6GT that would be good for SE operation in similar fashion with lower or similar wattage.
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Anyway the amp is not very loud but has a wonderful tone and quality to it. Still a little too loud
A VVR might resolve that for you? And it would reduce the 6K6 to a more appropriate plate voltage.
Tubenit
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I thought the 6K6GT was good to 350v on the plates?
Can you show me how to do the VVR on a BF Champ? I would appreciate that immensely. The concept sounds very good as it does not effect the preamp voltage nor gain/drive into the power tube which is my issue with master volumes on SE amps. That is if I have the concept of VVR correct.
I'm all about working with the landlord and not disturbing anybody. She said this guy was the only complaint on me in the 5 years she has been here. There are 6 floors and 20 apartments on each floor(10 per side) if 3.5 people lived in each apartment there would be approximately 400+ people in this building and nobody complained in the 8 years I have been living with my mom, since my dad passed. Before that they lived here 38 years. The whole complex probably houses at least 4000 people and this would be considered a small (privately owned) housing project in New York City(there used to be more when all the apartments were filled, they raised the rents too high now.). There are close to 500,000 people on Staten Island......no wonder New Yorkers have bad attitudes.
I'm going to drag my useless body to home depot tomorrow and buy some insulation for the closet in my bedroom to make a type of isolation area.
The VVR sounds like a good idea especially on some of the builds I already made that are done and working very well. But I was pleasantly surprised at how well the 6K6GT sounded.
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The Specs I find on the 6K6 have 315V max on the plates, and 285 on the screens. 8.5W plate & 2.8W screen dissipation.
In a SE setup, 100V on plate and screens, -7v bias, and a 12K plate impedance load, it will put out 0.35W.
In a SE setup, 315v plate, 250 screen, -21 bias, and a 9K plate impedance load, it will put out 4.5W
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I'm getting 8watts at 320V from my bias meter.
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Are you referring to plate dissipation?
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I've used a 6K6 in a Champ amp with great tonal results. (Didn't care about the voltage.)
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From Archives:
http://www.el34world.com/Forum/index.php?topic=6899.0
Just VVR the poweramp and leave the preamp alone, IMO. This is easy to install and is an inexpensive mod. The VVR can lower the 6K6 plates voltage and reduce volume.
With respect, Tubenit
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I thought the 6K6GT was good to 350v on the plates?
It is. I've also used 6K6's in a tweed Deluxe copy. I would hesitate at normal blackface voltage, but I've got enough of these tubes that I can afford to kill one or two in an experiment.
What Tubenit is saying is that the VVR is an adjustable way to reduce plate voltage, even down to pretty low levels.
Assume that the tube behaves in a linear fashion, so that if you reduce the supply voltage by half, the current is reduced by half. For a beam power tube or pentode, the reduction of screen voltage will result in reduced plate current. If you have a VVR and turn it to half, voltage is cut by half and current is cut by half. That results in 1/4 of the power output.
Don't be too slick and reduce only the screen voltage (except with different goals). If the plate voltage stays the same but just current is reduced by half, obviously you have 1/2 power instead of 1/4 power. Using the VVR to change both plate and screen voltage will likely give a more pleasing result.
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Awesome thanks guys!!!!!!!!!
I emailed Dana Hall about buying 2 of his VVR kits.
I'm using a compubias digital meter so I would guess that it's plate dissipation.
The trick is to get my sound/tone without too much compromise. If I don't get close enough I might as well use a PV solid state practice amp and be done with it. There is nothing like the glorious sound of a cranked tube amp whether it's 1 watt or 100 watts, I guess that's one reason we are all here.
Thanks again, of course I will probably have a zillion questions about other designs. Once I start on something I tend to get deeply involved. This might help others too. Plus I see PRR has a design with 6au6a tubes????
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More info on power section only VVR.
al
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> Don't be too slick and reduce only the screen voltage ...If the plate voltage stays the same but just current is reduced by half, obviously you have 1/2 power instead of 1/4 power.
But for _same_ load impedance, half-current is still quarter power. You are "wasting voltage", but you gonna waste voltage in any case (unless you develop a true variable-voltage power supply rather than a voltage-dropping PS).
In tests with near-constant plate voltage and variable G2 voltage, I got fairly good 'scope waveforms from 300V down to 20V-30V with power output very nearly as square of voltage, 13+Watts to ~~0.1W.
But even with 6K6 at max rating (like 3W output), this only gets you down to 0.03W. In a good guitar speaker this is 80dB. Which is louder than the average TV set normal level. And background TV is easier to ignore than wild geetar playing.
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And my geetar playing is pretty wild....... :laugh:.....not......I'm just a simple blues and blues rock player. I don't use a lot of distortion and wild effects nor drop D tuning and Van Halen dive bombing. The most rock stuff I do is Z.Z. Top or Rolling Stones type stuff, maybe some Lynard Skynard stuff(did I spell that right?).
Just got a Killer Ant today, I tried it. Half volume and it was pretty loud but nothing crazy. Not as loud as the 6K6 champ. Volume on max was too much drive for me, half way was in the right place.