I am designing a Hiwatt 50W guitar amp clone, so I am a bit concerned about the output transformer.
Originals used the famous Partridge irons, which are reputed to be quite hi-fi for guitar needs. I have seen a freaky frequency response for a 100W one somewhere. Anyway:
I was thinking about using a Hammond 1650KA for a 50W amp. Do you think it will compete against the Partridge in general? Has anyone ever compared them?
I would like to hear views on their quality in general - not only "for guitar purpose they are both wonderful". This is welcome too, though.
EDIT: Both subjective and objective opinions are welcome of course. "Heard both of them, they sound good" or "THD and response are..." are both useful!
Originals used the famous Partridge irons, which are reputed to be quite hi-fi for guitar needs. I have seen a freaky frequency response for a 100W one somewhere. Anyway:
I was thinking about using a Hammond 1650KA for a 50W amp. Do you think it will compete against the Partridge in general? Has anyone ever compared them?
I would like to hear views on their quality in general - not only "for guitar purpose they are both wonderful". This is welcome too, though.
EDIT: Both subjective and objective opinions are welcome of course. "Heard both of them, they sound good" or "THD and response are..." are both useful!
Partridge OPTs are sough after, especially for hi-fi designs. Hammond OPTs are great for guitar amps and are the workhorses of the industry, and they are a lot cheaper! If you want to do an exact clone, then you must use the Partridge otherwise stick with the Hammond. Is the amp for a client or yourself?
It is a clone for me. Of course I think about costs, that is why I thought about Hammond!
There are other options (Lundahl etc) that may be better, but cost twice as much.
I think that Hiwatts should be the first guitar amps to utilise a non-coloring OT. I suspect every other guitar amp uses an OT that does color the sound.
So in theory, every well designed OT should deliver the goods in my opinion. I ask to see whether this assumption has been realised in practice by anyone!
There are other options (Lundahl etc) that may be better, but cost twice as much.
I think that Hiwatts should be the first guitar amps to utilise a non-coloring OT. I suspect every other guitar amp uses an OT that does color the sound.
So in theory, every well designed OT should deliver the goods in my opinion. I ask to see whether this assumption has been realised in practice by anyone!
You want a full frequency band (hifi) output transformer made recently, look at these: DYNACO Replacement Transformers - MADE IN USA
St70 output transformer is 35 watt (6CA7) Mark IV is a little bigger.
St70 output transformer is 35 watt (6CA7) Mark IV is a little bigger.
Hiwatt OT clones for DR504 are 3.7k-3.8k primary. I can buy a Heyboer clone for a 50W for 140 euros. It is acceptable price, but I don't know if they are as good as the originals.
Hammond 1650KA is 50W, 3.4k primary, 30Hz-30kHz at +/-1db. I don't know anything about their THD specifications though. It costs 100 euros for me. Seems to be adequate for guitar use.
I definitely want a hi-fi OT for this amp. But I can't know whether the 1650KA is good enough or what.
I started looking at weight for some reason for various models. An original 100W OT Partridge weights about 7lbs, and Hammond 1650KA is specified at 2.8kg. Seems to be a big iron for the job.
Isn't Hammond OT acceptable for a hi fidelity system? Then it might be for me too. I don't think I am willing to pay more than 150 euros for something I might not hear. That's why I ask, is there any possibility (facts, please) that an expensive, wide BW OT will do better at 50Hz-15kHz than a Hammond? Because I think that this is a spectrum covering everything a guitar needs.
For instance, I could buy a Lundahl LL1620 for 300 euros. Is it worth it? A bit skeptical about that.
Hammond 1650KA is 50W, 3.4k primary, 30Hz-30kHz at +/-1db. I don't know anything about their THD specifications though. It costs 100 euros for me. Seems to be adequate for guitar use.
I definitely want a hi-fi OT for this amp. But I can't know whether the 1650KA is good enough or what.
I started looking at weight for some reason for various models. An original 100W OT Partridge weights about 7lbs, and Hammond 1650KA is specified at 2.8kg. Seems to be a big iron for the job.
Isn't Hammond OT acceptable for a hi fidelity system? Then it might be for me too. I don't think I am willing to pay more than 150 euros for something I might not hear. That's why I ask, is there any possibility (facts, please) that an expensive, wide BW OT will do better at 50Hz-15kHz than a Hammond? Because I think that this is a spectrum covering everything a guitar needs.
For instance, I could buy a Lundahl LL1620 for 300 euros. Is it worth it?
A bit skeptical about that.
But I need a 50W output transformer, for 2 EL34. And primary impedance is about 3.7k in original models, as I know. Doesn't this matter? I would be very happy to try the Dynaco solution, but I don't know if it will fit my circuit's needs!
EL34 was the small glass European version of the GE 6CA7. What the ST70 came with.
And a PASIV transformer A431S at triodeelectronic.com, for "60 W 4300 ohm" is $137 or about 100 euros, plus freight and import duty. the A470S 35 W for the ST70 (6CA7) is $115 or about E85.
Lower impedance on the A431S means your tube plates should last longer than original.
My original ST70 with good B+ from the stock filter cap and fresh rectifier and output tubes, will put out 17.5 VAC on an 8 ohm resistor. You may calculate the watts. After about 10000 hours or 8 years use, the rectifier tube needs replacing for low voltage at high volume. B+ cap is changed at the same time. At about 10 years, the power tubes become the limitation. Guitar results may be less hours; I run at typical volume of 2 Vac, or silence a lot of the time the amp was on.
And a PASIV transformer A431S at triodeelectronic.com, for "60 W 4300 ohm" is $137 or about 100 euros, plus freight and import duty. the A470S 35 W for the ST70 (6CA7) is $115 or about E85.
Lower impedance on the A431S means your tube plates should last longer than original.
My original ST70 with good B+ from the stock filter cap and fresh rectifier and output tubes, will put out 17.5 VAC on an 8 ohm resistor. You may calculate the watts. After about 10000 hours or 8 years use, the rectifier tube needs replacing for low voltage at high volume. B+ cap is changed at the same time. At about 10 years, the power tubes become the limitation. Guitar results may be less hours; I run at typical volume of 2 Vac, or silence a lot of the time the amp was on.
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Little side note some early Sunn Amps basically had the entire Dynaco MKIII Power Amp section running the outputs including the OTs. Check pricing on Edcor, they wind to customer specs for both guitar and audio amps, and the pricing looks generally good. Couple of guys running those at Burning Amp, and to me they sounded very nice.
Won't a different turns ratio in output transformer affect the amp tonally, in that it will alter the current demand from the output tubes? How about the load line? Or will a 3.8k to 4.3k difference mean nothing?
If it is insignificant, I am willing to try Edcor or Dynaco.
EDIT: Multiple secondaries can always be an advantage too, to try out different cabs. Hammond ones have 4, 8 and 16 ohm taps.
If it is insignificant, I am willing to try Edcor or Dynaco.
EDIT: Multiple secondaries can always be an advantage too, to try out different cabs. Hammond ones have 4, 8 and 16 ohm taps.
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imho, it will not sound significantly different from 3.8 to 4.3K. You could adjust on bias but I don't see it changing sound much. What is significant on audio grade OT is they are generally flat response (dynaco flat to 1db from 10-20KHz) so there is that transparency with very little coloration from the transformer.
I see. How about the Edcor irons? They have 4, 8, 16 ohm taps which is very good and shipped, they cost as much as a Hammond.
An example that seems to fit my needs:
https://www.edcorusa.com/p/447/cxpp60-ms-4k
It looks good to me, and you have the ultra-linear taps as an option if you want to use a backpanel switch to run the EL-34s like that. Maybe you can get some more feedback here as to their service, I have not bought from them yet, but price looks good, and they sounded good in hi-fi to my ears.
The amp could be flat out to 50kHz if you wanted, but guitar speakers roll off in the 3k-5kHz area, so not sure what all that high end flatness would get for you. You don;t see tweeters on guitar speaker cabinets.
Bandwidth is great for hifi, but if you are building a guitar amp rather than a PA amp, remember a guitar amp is PART of the instrument. A hifi is designed to faithfully REproduce the source material and add nothing of its own. That is why within their capabilities, hifi amps and PA system amps all sound alike. But a guitar amp is specifially designed to add its own character to the sound, they are by their nature anything BUT hifi. That is why one player plays a Marshall, and another player plays a Fender. They sound different, and that is the point. The guitar amp is not meant to simply reproduce a source, it is there to amplify and modify the source material.
Transformers do sound different from one another, but I don;t think bandwidth is the issue, response curves matter more.
Bandwidth is great for hifi, but if you are building a guitar amp rather than a PA amp, remember a guitar amp is PART of the instrument. A hifi is designed to faithfully REproduce the source material and add nothing of its own. That is why within their capabilities, hifi amps and PA system amps all sound alike. But a guitar amp is specifially designed to add its own character to the sound, they are by their nature anything BUT hifi. That is why one player plays a Marshall, and another player plays a Fender. They sound different, and that is the point. The guitar amp is not meant to simply reproduce a source, it is there to amplify and modify the source material.
Transformers do sound different from one another, but I don;t think bandwidth is the issue, response curves matter more.
I have been using the A470S Dynaco replacements from Triode for about 12 years in my guitar amps. With a pair of EL34s, I am getting 40Watts at the onset of clipping into 8 ohms with SED tubes with my design. (They are not Hiwatt clones.) The 35W spec is for 20Hz. They can easily do 50W (or more) at 80Hz.
Love the sound.
Love the sound.
Thank you all!
Enzo, it may seem weird, but tone is exactly why I need a hi-fi OT. Seriously: a Hiwatt amp's tone is heavily based (rumor has it) on the high quality of its output transformer. So, for me to achieve the tone of a Hiwatt, I must ensure that all that tone comes from before the output iron - this is exactly the logic of this amp.
These Partridge transformers were hi-fi at least, according to measurements. So, it seems to be an "easy" deal for me: to get the tone, I should get an OT that is just flat and good!
I agree on the bandwidth, that is why I proposed the 1650KA solution. I assume that a transformer flat in the region of say 50Hz-15kHz (and as you said, probably only 10kHz or 5kHz) should do the job.
I am willing to seriously consider these Dynaco clones, many thanks for recommendation. Still a bit concerned about 4.3k primary impedance, maybe this could play a bigger role in the tone coloration of the amp considering its inherent design "flaws" compared to a genuine hi-fi design. But I am not very familiar with tube output stages yet, so I don't know whether this can be dealt with by means of altering bias.
Enzo, it may seem weird, but tone is exactly why I need a hi-fi OT. Seriously: a Hiwatt amp's tone is heavily based (rumor has it) on the high quality of its output transformer. So, for me to achieve the tone of a Hiwatt, I must ensure that all that tone comes from before the output iron - this is exactly the logic of this amp.
These Partridge transformers were hi-fi at least, according to measurements. So, it seems to be an "easy" deal for me: to get the tone, I should get an OT that is just flat and good!
I agree on the bandwidth, that is why I proposed the 1650KA solution. I assume that a transformer flat in the region of say 50Hz-15kHz (and as you said, probably only 10kHz or 5kHz) should do the job.
I am willing to seriously consider these Dynaco clones, many thanks for recommendation. Still a bit concerned about 4.3k primary impedance, maybe this could play a bigger role in the tone coloration of the amp considering its inherent design "flaws" compared to a genuine hi-fi design. But I am not very familiar with tube output stages yet, so I don't know whether this can be dealt with by means of altering bias.
I would be supprised if the 4.3K vs 3.8K (or so) would make much difference in the tone. The bias can have an impact on the tone in many designs. I like the sound of slightly warmer biasing (hence only 40Watts - slightly closer to the Class A side of Class AB). Depending on the desired sound of the folks playing my amps, I bias anywhere from 35ma to 45ma. Playing style has a lot to do with this preference. Higher bias tends to wear the tubes out faster
There is a cost to everything!
There is a cost to everything!
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