Got this guy AS-2T230 - 200VA 230V Tube Transformer - AnTek Products Corp MAybe an overkill, but.. 
Hey, thanks for offering, but it doesn't look like I have an access to see it.
Got this guy AS-2T230 - 200VA 230V Tube Transformer - AnTek Products Corp MAybe an overkill, but..
Code:
ELECTRICAL CHARACTERISTICS
Outputs 4x
Power 200VA
Output Voltage Current
230V 0.4A
230V 0.4A
6.3V 4A
6.3V 4APlease note that you need to have another secondary 50 V 100 mA to supply:
- the negative side of the PI
- the negative side of the PowerDrive
- the fixed bias
- the positive side of the PowerDrive
This will give you around -35 Vdc and +35 Vdc, based on it you can look at the table I posted and select the right resistor for the R16 and R17 mod.
Very good point! I have small 60V toroids for this purpose.
I thought 100 ma is probably generous. Out of curiosity, what is the required minimum current capability for such transformer shown by your simulations? I know 5VA is about a small as transformers go.
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Circuit changes for 12AT7 substitution
My BabyHuey is now 6 years old.
I built the circuit that is version 1.1 as shown in the wiki page. I changed the Hammond output transformers to some from James. The specs of those transformers are supposedly better in terms of bandwidth, but my real motivation is that they look prettier. It is connected to Alpair10s full range drivers and it behaves nicely.
Aside from a single early incident of a suddenly failed EL84 and a dry joint I had to touch up a few months ago, it has worked without hiccup.
So I decided to poke at it
I have never really needed to run it at anything more than 25% on the volume dial so I'm not stuck for gain.
I decided to change the two 12AX7 to 12AT7 (ECC83 to ECC81) to see if the supposed higher bandwidth made much of a difference. I'm not expecting to be able to hear anything beyond about 15kHz, but I do think that the transient response is subtly different; I think it made it a little more transparent. Maybe it is just the Ikea effect, but no matter, I'm happy with how it sounds.
Now, the question. I made zero changes to the rest of the circuit, I just swapped out the tubes. While the tube spec change is not a huge one, I'm sure that the biases and loads are not exactly as they should be. Is anyone able to shed some light on what else I should change to better match 12AT7s?
My BabyHuey is now 6 years old.
I built the circuit that is version 1.1 as shown in the wiki page. I changed the Hammond output transformers to some from James. The specs of those transformers are supposedly better in terms of bandwidth, but my real motivation is that they look prettier. It is connected to Alpair10s full range drivers and it behaves nicely.
Aside from a single early incident of a suddenly failed EL84 and a dry joint I had to touch up a few months ago, it has worked without hiccup.
So I decided to poke at it
I have never really needed to run it at anything more than 25% on the volume dial so I'm not stuck for gain.
I decided to change the two 12AX7 to 12AT7 (ECC83 to ECC81) to see if the supposed higher bandwidth made much of a difference. I'm not expecting to be able to hear anything beyond about 15kHz, but I do think that the transient response is subtly different; I think it made it a little more transparent. Maybe it is just the Ikea effect, but no matter, I'm happy with how it sounds.
Now, the question. I made zero changes to the rest of the circuit, I just swapped out the tubes. While the tube spec change is not a huge one, I'm sure that the biases and loads are not exactly as they should be. Is anyone able to shed some light on what else I should change to better match 12AT7s?
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Very true, but psupine claims he's using 12AT7 since 6 years now, and he prefers that tube. Also because he plays at no more than 1/4th of the volume.
It seems legit to me to ask if there's any way to improve his own system even if not as per original design.
BH is quite an open source project since the very beginning.
It seems legit to me to ask if there's any way to improve his own system even if not as per original design.
BH is quite an open source project since the very beginning.
Thanks all for your replies.
I have the adjustment pots and a meter built into my front panel (see post#1478) so it's very easy to change the balance there, and I do this as a regular check. It's interesting that the correct setting changes as the amp warms up, but it's very consistent when settled.
I have been using 12AX7s for the last six years. I initially had Mullards, but then moved to Genelex which sound a little clearer than the Mullards. I'd say the Mullards were warmer, so it all depends on the sound one is chasing. Personally, I'm interested in clarity over warm colouring, so in a way I'm trying to make my tubes sound solid state. (The shame!). I have been happy with the Genelex 12AX7s but I thought I'd try the ATs as an experiment.
The 12AT7 tubes are pretty 12AX7ish. As zintolo noted, gain is not an issue for me, but the higher current might be an issue.
Zintolo, thanks for the offer of simulation. If you have simulation results on reducing or removing the global feedback, I'm interested in that too. I'd trade THD for transient accuracy.
I have the adjustment pots and a meter built into my front panel (see post#1478) so it's very easy to change the balance there, and I do this as a regular check. It's interesting that the correct setting changes as the amp warms up, but it's very consistent when settled.
I have been using 12AX7s for the last six years. I initially had Mullards, but then moved to Genelex which sound a little clearer than the Mullards. I'd say the Mullards were warmer, so it all depends on the sound one is chasing. Personally, I'm interested in clarity over warm colouring, so in a way I'm trying to make my tubes sound solid state. (The shame!). I have been happy with the Genelex 12AX7s but I thought I'd try the ATs as an experiment.
The 12AT7 tubes are pretty 12AX7ish. As zintolo noted, gain is not an issue for me, but the higher current might be an issue.
Zintolo, thanks for the offer of simulation. If you have simulation results on reducing or removing the global feedback, I'm interested in that too. I'd trade THD for transient accuracy.
I am just starting to collect the parts to build the BH and was curious if the 12AT7 might work. I have bought a few types of 12AX7, so will stick to them first. I have tried to make a few summary notes of this massive and confusing thread, but am sure I will have plenty of questions along the way.
.. dB
.. dB
I still haven't built my BH84 yet but based on my experience with 12AT7's and 12AX7's I would not prefer an 12AT7 generally.
I have built a Tubelab SPP that uses 12AT7's and while the amp sounds very good its not easy to come by good 12AT7's (production quality is not as consistent). I've tried many types too.
For the 12AX7's on the other hand, there are so many very good types available. Telefunken, Valvo, Amperex, RCA, etc ... and the fact that it is better in this curcuit makes it an obvious choice.
For what its worth, I've refurbished a Sherwood S-5000 II amp that had Mullard 12AX7's for the phase inverter and gain stages. The Mullards do sound a bit muddy (dark you could say). Changing to more "inferior" 1970's Sylvania tubes sounded better.
psupine, if you've only tried the Mullard 12AX7's for NOS and then new production Genalex, then it could also be worth trying others such as the Telefunken's, Amperex Heerlen or 1950-1960's RCA.
Since I haven't built the BH84 I don't know how much the input tube influences the sound, I'm sure the overall signature also depends on the output transformers and perhaps power tubes.
I have built a Tubelab SPP that uses 12AT7's and while the amp sounds very good its not easy to come by good 12AT7's (production quality is not as consistent). I've tried many types too.
For the 12AX7's on the other hand, there are so many very good types available. Telefunken, Valvo, Amperex, RCA, etc ... and the fact that it is better in this curcuit makes it an obvious choice.
For what its worth, I've refurbished a Sherwood S-5000 II amp that had Mullard 12AX7's for the phase inverter and gain stages. The Mullards do sound a bit muddy (dark you could say). Changing to more "inferior" 1970's Sylvania tubes sounded better.
psupine, if you've only tried the Mullard 12AX7's for NOS and then new production Genalex, then it could also be worth trying others such as the Telefunken's, Amperex Heerlen or 1950-1960's RCA.
Since I haven't built the BH84 I don't know how much the input tube influences the sound, I'm sure the overall signature also depends on the output transformers and perhaps power tubes.
I completely agree. Just trying to point out that replacing the 12AX7 with a 12AT7 might compromise the synergies in the original design.
Would you be able to post your simulation please? I've attached mine but I don't believe the 7.5% THD figure. I've used a different FET in the model because I don't have a model for the STU9H65M2. I've incorporated your recommendations for the differential pair CCS. I can post the additional models if there's interest.
I've just started building my EL84 BH. It'll be a while before I can test it after I baulked at the US$45 shipping quote for 4 EL84s.