luvdunhill Posted December 4, 2007 Report Posted December 4, 2007 just curious, has anyone tried using other tubes in the Blue Hawaii than the 6CA7/EL34? I ended up with a set of boards, and was looking at some datasheets over the weekend. I started looking at the 6BG6GE, 3D21A/WB/7403, 12E1, EL360, 6146, etc.... I started looking more at the 3D21A, but noted that the one major concern is that the transconductance is about half that of the EL34 which means that the gain will probably be about 6dB lower than the EL34, and depending on headroom in the cathode drive circuit this could result in significantly higher distortion. (Also, I might not get enough voltage swing without making other changes that would raise the source impedance of the amplifier.) Other specifications seem reasonable, but I can at best make a guess as to its suitability as there are no triode curves provided for this type. Then I looked at the 6BG6GE which seems like it might work, but has some of the same concerns as above.... Both of these two tubes look like good starting points... anyways, has anyone gone down this path?
pabbi1 Posted December 8, 2007 Report Posted December 8, 2007 I looked at the KT77, which LOOKS like a direct, but who knows? Other than the new production JJ, there is only the old Gold Lions, and VERY pricey... calling Spritzer or Justin.
NotoriousBIG_PJ Posted December 8, 2007 Report Posted December 8, 2007 Get the jj kt77's. They sound better than any current production el34. Biggie.
spritzer Posted December 8, 2007 Report Posted December 8, 2007 You certainly could alter the circuit a bit and install different tubes but none of them sound as good as the EL34. Since we are on the subject of pentodes I just bought a quad of JAN 807's and I'm going to see if I can't throw something together.
kevin gilmore Posted December 8, 2007 Report Posted December 8, 2007 I'm pretty sure i tried kt77's at one point, the skinny bottle versions should be a complete identical replacement. (I think, don't really remember) el360's are virtually impossible to find, and when you do they are chinese junk and the top cap likes to come off. kt88's, 6l6's and things like that seem a bit ratty when you run them all the way to 800 volts.
luvdunhill Posted December 8, 2007 Author Report Posted December 8, 2007 can circuit can handle only having half the transconductance of the EL34? This is the only spec that I cannot meet easily. see my concerns above. none of the tubes I listed are drop-in replacements. That would be too easy... I agree about kt88, 6l6, etc... I won't be trying those. EL360 are getting hard to find, but I have some sources. Again, not my first choice, but they look promising. <flame suit on>I'm more tempted to play with the 3D21A after hearing these in Mikhail's ES amps (in direct comparison to the Mullard EL34 actually). Amazing tubes and the 3D21WB are pretty much indestructible... perfect for the BH + big heatsinks + IXYS current sources.</flame suit on> Looks like there is only one way to find out...
luvdunhill Posted December 9, 2007 Author Report Posted December 9, 2007 You certainly could alter the circuit a bit and install different tubes but none of them sound as good as the EL34. this is a rather ambiguous statement. do you mean: a.) the EL34 is the best sounding pentode b.) the EL34 is the best sounding pentode in the BH circuit c.) the EL34 is the best sounding pentode in the BH circuit that is pinout compatible with the original circuit
kevin gilmore Posted December 9, 2007 Report Posted December 9, 2007 Looks like there is only one way to find out... Actually there are 2 ways. You do it, or you get someone to do it for you. The 3d21's would definitely work in a BH. But really they want to be run at 1kv+ and then you have to put current sources in series or otherwise they smoke.
spritzer Posted December 9, 2007 Report Posted December 9, 2007 this is a rather ambiguous statement. do you mean: a.) the EL34 is the best sounding pentode b.) the EL34 is the best sounding pentode in the BH circuit c.) the EL34 is the best sounding pentode in the BH circuit that is pinout compatible with the original circuit I'm always ambiguous... The EL34 is far from being the best pentode out there but a Mullard XF2 is a force to be reckoned with. Expensive as hell so I'm all for a cheaper type that sounds as good so please do some testing... since I can't be bothered to butcher my BH. Btw. Kevin have you finished the 845 based amp circuit yet. I'd really like to see it when you do.
luvdunhill Posted December 11, 2007 Author Report Posted December 11, 2007 You certainly could alter the circuit a bit and install different tubes but none of them sound as good as the EL34. Since we are on the subject of pentodes I just bought a quad of JAN 807's and I'm going to see if I can't throw something together. spritzer: A standard 6BG6 is an 807 with an octal base on it, so perfect for dropping into the BH. There have been reports of Philips/ECG 6BG6GA tubes that can be run at (a minimum) 500VDC plate voltage, 75ma plate current (35W) with screen voltage set at 450 VDC and can replace an EL34 where the cathode is connected to the suppressor grid, like in the BH. This will be the first place I'll start, as these are cheap and reportedly sound great. KG: I don't see any reason I cannot also increase the voltage of the positive rail (as well as increasing the current through the programmable current sources) for more power? My psu can easily accommodate raising just the +400 V rail... I figure maxing out what my psu can deliver voltage-wise and then varying the current sources until I get 35W and seeing what happens then... KG: do you have an opinion on DC heaters employing things like hum balancers or cathode biasing? I found someone selling little PCBs to do the trick: http://www.tubeaudiokits.com/LIBRARY/heater-balancer.htm
spritzer Posted December 11, 2007 Report Posted December 11, 2007 The 807's aren't cheap, they're dirt cheap. I bought them to build a cheap P-P speaker amp that could serve as a Stax amp but now I'm tempted to test them in the BH circuit... \
luvdunhill Posted December 12, 2007 Author Report Posted December 12, 2007 The 807's aren't cheap, they're dirt cheap. I bought them to build a cheap P-P speaker amp that could serve as a Stax amp but now I'm tempted to test them in the BH circuit... \ The uprated 6BG6 are $6 each... them's US dollars... that's basically free My guess is without upping the bias, the difference in transconductance will be too great to be able to accurately judge the new tubes. That's why I have two 16" pieces of this due to be here on Friday
spritzer Posted December 12, 2007 Report Posted December 12, 2007 Ahhh since its in US$ you get payed by the seller to be rid of them...
kevin gilmore Posted December 12, 2007 Report Posted December 12, 2007 If you are going to try DHT's, you are going to have to have 4 completely seperate filament power supplys. Reason, 50 volts of audio on the cathode and opposite in phase with the other tube in the same channel.
spritzer Posted December 12, 2007 Report Posted December 12, 2007 If you are going to try DHT's, you are going to have to have 4 completely seperate filament power supplys. Reason, 50 volts of audio on the cathode and opposite in phase with the other tube in the same channel. That's what I was planning to do, running every tube off its own PSU. The cost isn't really an issue here but I'd like to use DHT's that are relatively cheap which the 845's aren't NOS. With my headphone collection almost complete it's time to build an amp to drive them all.
kevin gilmore Posted December 12, 2007 Report Posted December 12, 2007 KG: I don't see any reason I cannot also increase the voltage of the positive rail (as well as increasing the current through the programmable current sources) for more power? My psu can easily accommodate raising just the +400 V rail... I figure maxing out what my psu can deliver voltage-wise and then varying the current sources until I get 35W and seeing what happens then... Raising one voltage does you no good. You have to raise both of them. If you replace the 2sa1156's with 2sa1413's then you can get to +/-550 Or if you replace the 2sa1156's with 2sa1968's you can probably get to +/-700
luvdunhill Posted December 12, 2007 Author Report Posted December 12, 2007 Raising one voltage does you no good. You have to raise both of them. If you replace the 2sa1156's with 2sa1413's then you can get to +/-550 Or if you replace the 2sa1156's with 2sa1968's you can probably get to +/-700 seems to me to be more complex that just swapping out the transistors. Won't I have to recalculate the resistor values for the vbe multipliers in the second stage, or will they still create the 13 v bias for the third stage? The 2sa1156 is a new one for me, I guess the fact that it is surface mount really isn't of any concern, as I wouldn't have to heatsink it anyways? Thanks for the heads up! will the power dissipation for the FETs remain about the same, or will I need to look into some extra heatsinking for them as well?
kevin gilmore Posted December 12, 2007 Report Posted December 12, 2007 You can make the 6.8k resistor a 10k pot, that should give you more than enough range.
Icarium Posted December 12, 2007 Report Posted December 12, 2007 I do love me the 3D21 types. Even Neil feels its a toss up between xf2s and the 3D21B.
luvdunhill Posted December 12, 2007 Author Report Posted December 12, 2007 You can make the 6.8k resistor a 10k pot, that should give you more than enough range. so, all the voltages would scale up in the output stage, so I can keep the 100V zener, the 50K at the bases of the 2sa1156 (soon to be 2sa1413/2sa1968) .. looks fun
luvdunhill Posted December 12, 2007 Author Report Posted December 12, 2007 I do love me the 3D21 types. Even Neil feels its a toss up between xf2s and the 3D21B. yeah I've heard them too I agree with KG, they need double the voltage (at least).
luvdunhill Posted December 30, 2007 Author Report Posted December 30, 2007 KG: Is it possible to put two IXCP10M45S in series and get double the current, but the same voltage rating as a single IXCP10M90S? I don't see why not, but figured I'd ask.
Elephas Posted December 31, 2007 Report Posted December 31, 2007 A local shop is selling these 4699 metal-base tubes and adapters. They claim it can be used in place of the EL34. I don't have an amp using the EL34 yet.
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