I'm putting together parts for my Liverpool combo build and thinking about adding in a half power switch. I've read it doesn't make a whole lot of difference in volume, but since I'm using VVR2 I'm not really concerned with volume. More of a tone shaping option.
So, the Toneslut OT has a 5.2K and 6.6K primary for EL84s or 6L6. I'm curious this OT in general and about keeping this OT with only the 5.2K tap on half power.
The impedance should be 8k for a pair, and 4k for a quad. Do you all use the 5.2K tap for your full power Liverpool builds? Must sound good if that's how KF did it. Wouldn't it be better if I"m using half power, to rematch the impedance on the OT to a pair of EL84? I know in the Matchless DC30 there is no OT tap switching and that's part of the sound shaping. I guess I'm curious as to what would sound better: a pair at 5.2k, 8k or 10.2k; a quad at 5.2k or 4k?
Do you know of any trannys with either a 4k/8k or a 5.2k/10.4k dual tap? I know Dana has had some custom wound by Heyboer, so I might consider getting one wound if the price is right.
Thanks guys for any help. My parts are slowly coming in. Got a chassis coming from Dana and boards from Joebob. Mouser order coming soon. Still have to decide where to get a 2X12 combo cab from.
Liverpool 1/2power and OT taps (suggestions)
Moderators: pompeiisneaks, Colossal
Re: Liverpool 1/2power and OT taps (suggestions)
You could go with the standard 5.2k and re-lable your secondarys 8/16/32 instead of 4/8/16 As long as you aren't wiring the combo cab for 4 ohms you should be good.soma_hero wrote:any ideas?
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Re: Liverpool 1/2power and OT taps (suggestions)
Soma,
Since you kinda already colored outside the lines by building the Liverpool in a combo, it seems your not a Trainwreck purist. That makes the half power option a reasonable thing to do. I have done it on two different Rocket builds and I'm quite pleased with the results. One of those used the Heyboer 5200 OT.
It has been said that the half power option creates a different amp... which sounds like what your after anyway. With the flip of a switch you have a different amp, what's not to like?
My experience says you are correct in believing the amp won't be substantially quieter, but I have found that it will be measurably and noticeably quieter. Also my experience with the Rocket amps was that if anything was disappointing about the half power option it was that the amp sounded too similar in either position.
Understanding transformers is art & science and IMHO, the ears are the best tools in either case. UR12 has confirmed the math for us... you're right 4K Ohms in & 4 Ohm out is fundamentally equivalent to 8K Ohms in & 8 ohms out. By the way, UR12 has posted some great results of 2-EL84 output tube Wreck type circuits.
Additionally there is a frequency dependent component for every transformer and I'll over simplify that by saying - "some sound better with the 4K/4 setup as opposed to the 8K/8 setup". Again, the ears will help you realize the best match... and sometimes both are going to sound quite good.
I've been sorting through transformer theory a bit and if I'm not entirely mistaken, it's something like the following (you might already know this) - There is sometimes a misconception that a given set of tubes/speakers/transformers have a steady state impedance... but in reality, the impedance value is a moving target, and "official" circuit impedance is really more like an average value. For a transformer, the ratio of input to output is always the same. The transformer doesn't actually have an impedance, but rather serves as a delivery mechanism that is always at a a constant ratio. The tubes on one side and the speaker on the other determine the circuit impedance. It is fair to say that some transformers are "happiest" within a given impedance range and that is typically why they are given an impedance rating.
Finally, It's in Gerald Weber's first tube amp book he mentions a rule of thumb that you can generally use a transformer and speaker combination within 100% of their impedance ratings. To say it another way, it you've got a 4 ohm output and put an 8 ohm speaker on it, it will likely not cause any ill effects. This rule of thumb does fall apart if the impedance gets too low - I wouldn't put a 2 ohm load on a 4 ohm output for instance, but it gives you a general idea for safe operating practices.
With a Heyboer 5200 output tranny at 5.2K Ohms, you're in very safe operating space with either 4 or 2 output tubes. For my own builds, the 5200 is one of the very best sounding transformers for EL-84's in pairs or quads.
You can buy 5200 trannies one at a time from Mojotone, or if I understand things correctly, the Toneslut output tranny is the same tranny with both a 5.2K and a 6.6K tap. Several of us keep a small stock of various Wreck friendly trannies around and if you dig through the posts, you'll find a wealth of info on what has been tried successfully and otherwise.
Cheers,
rj
Since you kinda already colored outside the lines by building the Liverpool in a combo, it seems your not a Trainwreck purist. That makes the half power option a reasonable thing to do. I have done it on two different Rocket builds and I'm quite pleased with the results. One of those used the Heyboer 5200 OT.
It has been said that the half power option creates a different amp... which sounds like what your after anyway. With the flip of a switch you have a different amp, what's not to like?
My experience says you are correct in believing the amp won't be substantially quieter, but I have found that it will be measurably and noticeably quieter. Also my experience with the Rocket amps was that if anything was disappointing about the half power option it was that the amp sounded too similar in either position.
Understanding transformers is art & science and IMHO, the ears are the best tools in either case. UR12 has confirmed the math for us... you're right 4K Ohms in & 4 Ohm out is fundamentally equivalent to 8K Ohms in & 8 ohms out. By the way, UR12 has posted some great results of 2-EL84 output tube Wreck type circuits.
Additionally there is a frequency dependent component for every transformer and I'll over simplify that by saying - "some sound better with the 4K/4 setup as opposed to the 8K/8 setup". Again, the ears will help you realize the best match... and sometimes both are going to sound quite good.
I've been sorting through transformer theory a bit and if I'm not entirely mistaken, it's something like the following (you might already know this) - There is sometimes a misconception that a given set of tubes/speakers/transformers have a steady state impedance... but in reality, the impedance value is a moving target, and "official" circuit impedance is really more like an average value. For a transformer, the ratio of input to output is always the same. The transformer doesn't actually have an impedance, but rather serves as a delivery mechanism that is always at a a constant ratio. The tubes on one side and the speaker on the other determine the circuit impedance. It is fair to say that some transformers are "happiest" within a given impedance range and that is typically why they are given an impedance rating.
Finally, It's in Gerald Weber's first tube amp book he mentions a rule of thumb that you can generally use a transformer and speaker combination within 100% of their impedance ratings. To say it another way, it you've got a 4 ohm output and put an 8 ohm speaker on it, it will likely not cause any ill effects. This rule of thumb does fall apart if the impedance gets too low - I wouldn't put a 2 ohm load on a 4 ohm output for instance, but it gives you a general idea for safe operating practices.
With a Heyboer 5200 output tranny at 5.2K Ohms, you're in very safe operating space with either 4 or 2 output tubes. For my own builds, the 5200 is one of the very best sounding transformers for EL-84's in pairs or quads.
You can buy 5200 trannies one at a time from Mojotone, or if I understand things correctly, the Toneslut output tranny is the same tranny with both a 5.2K and a 6.6K tap. Several of us keep a small stock of various Wreck friendly trannies around and if you dig through the posts, you'll find a wealth of info on what has been tried successfully and otherwise.
Cheers,
rj
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Re: Liverpool 1/2power and OT taps (suggestions)
Thanks for the response RJ, much appreciated!
From what I've read and understood about output transformers and plate loads, the reflected impedance is as important as the tap on the OT, so what Dana has suggested is probably just what I'll do. I'll use the Toneslut tranny with the 5.2k tap and just adjust the speaker loads to match the impedance if I think it needs it.
Letting the ears do the work.
From what I've read and understood about output transformers and plate loads, the reflected impedance is as important as the tap on the OT, so what Dana has suggested is probably just what I'll do. I'll use the Toneslut tranny with the 5.2k tap and just adjust the speaker loads to match the impedance if I think it needs it.
Letting the ears do the work.