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Hashimoto and the wonderful 45

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Most have probably noticed I like the 45 triode... and have a large collection of them, 20+ pairs... different brands and different internal structures, most in ST glass. I do have a couple pairs of RCA Balloon glass but there are two different internal structures on these as well. I even have a matched pair of new manufacture EML45 tubes. Overall, my favorite 45 is ST glass with a specific internal structure (note, not brand). As much as I've played with the balloon glass, they always have more output hum and are always more sensitive to mechanical vibration.

Of the ST glass versions, I have branded glass in RCA, Philco, Tung-Sol, Ken-Rad, GE, Sylvania, National Union and Zenith. I think most people realize that tube manufacturers frequently sourced tubes from one another due to the simple practicalities of setting up a manufacturing line to produce a specific tube type. As a result, it's not always clear who made the 45 you're holding. With brands like Zenith, they didn't actually make any tubes (at least according to my late uncle who was a long time Zenith dealer dating back to the 50's until he retired and moved to Florida). Depending on contracts they probably used Sylvania or RCA... maybe others.

My current personal SET amplifiers are based entirely on Hashimoto transformers. These are all hand-made in Japan and as many may know, are a spin-off from the old Sansui company... and included design plans, patents, technology, the plants and the people. I consider them to be some of the finest iron you can get at any price but everyone has their favorite iron vendor and there's plenty of great stuff being made today. I also have MQ iron and have Mike making some custom RH40 units for me now for another 45 project, so I'm not totally myopic on this.

I've used these amplifiers to do extensive testing on my 45 collection and have concluded that a specific internal structure is better than the rest. And you can also find two slight differences in the internal structure here too. From what I can tell, this particular version was made by Sylvania or Ken-Rad... I just can't be sure. In any case, I've found identical internal structured 45s labeled from Ken-Rad, Sylvania, Philco, RCA, Tung-Sol and Zenith. One thing is certain, they are not made by RCA... as the real RCA 45 has a full circular top mica insulator. The ones I prefer have a circular top insulator with two sides cut flat and with twin support wires which extend past the mica and firmly rest against the glass envelope. They also have added rivets on the top insulator which stiffen the mica support to the vertical support wires.

So, why do I prefer these over the others? Simple... measurements first. Using this particular type, I have consistently found that they are less sensitive to mechanical vibration (some 45s will react to a hand-clap a few feet away and tapping the chassis can really set them off), I can measure less distortion than others (on a calibrated HP 334A analyzer) and I can get better hum balance for improved signal to noise ratio. The best ones I have can be measured below 150 microvolts output noise using an AC filament supply. One fact that supports this is that the actual branding on the base means nothing... doesn't matter if it says Philco, RCA, Sylvania or Joe's garage. The listening test also confirms my choice on this particular variation of the 45. I actually have a NIB pair of RCA 45s with identical codes on the base... one is a real RCA made and the other is my preferred version... now how do you suspect that happened??

The matched pair of 45s I'm currently running in my amps are actually branded Zenith and were NIB. One nice thing about Zenith is they spec'd their tubes very tightly and required the vendor to meet a rigid specification as Zenith was a premium brand in it's heyday. When you bought a Zenith branded replacement for your Zenith set, there was no issue as to whether it would perform. I've attached a pic of the amplifier below which shows a Ken-Rad 45... these are now my backup pair for the amplifiers but have the identical internal structure.

An externally hosted image should be here but it was not working when we last tested it.

If you look closely you can see the top mica insulator and the two flat sides along with the rivets for additional support. I think many people associate some of the characteristic sounds of warm, smooth, etc. to 45 triodes which are sensitive to mechanical vibration... even the music itself will affect poor ones. I'll get some better pics of the various 45 internals and post them at a later date.

I would be interested to hear about anyone else's experience with the 45 of course.... and if you have found a specific version of the 45 that you prefer, please share it.

Regards, KM

I am also using a 45 amp with hashimoto transformers providing duty for my D5nf. I do not have a large collection of 45 brands (so far all ST shape - RCA, Ken-Rad, Tungsol and Sylvania).Of these, i liked the Sylvanias best. They are of the same partial circular top insulator and twin support wires construction that you described. Coincidentally, my only tungsol pair are of the same construction. I believed this particular tungsol were manufactured by sylvania as from what I observed, sylvania made 45 tubes have a trademark hexagon shape and three alphanumeric date code stamped on the glass.


I’m sorry to drag up this thread but thank you for sharing your findings. I’m actually in the process of collecting parts for a 71A amp and was also planning on the Hashimoto transformers. I was also planning to use the same transformer for a SE 45 amp I may build later down the track.

I first considered the H-507S but noted that the H-20-7U has slightly better specs, especially in regard to bass response. But I’m not sure if the significant upgrade (in spec and price) from H-507S to H-20-7U will have many benefits for amps producing only 0.7 to 2 watts.

Kmaier, I noted in another post that you are using the H-507S and you are rather content, did you consider the H-20-7U?

Any advice or suggestions would be most appreciated


I just went with Hashimoto H-20-7U for 1 watt amp, albiet it will also have O-Netics level II IT's. But will let you know how the H-20-7U sound. I should have them by next week & am ready for install. I struggled with same delima, so I flipped a coin in my head & called Isao Asakura & placed the order. Now I can relax.
J & G
Hey Richard,
Yes the versitility of the H-20-7U is nice. One other thing to say about Hashimoto is that there cores are Japanese as entire materials & labor to build them, they are done by hand. I was concerned about China cores bieng used, but when directly asking Isao Asakura, who visits the plant a couple times a year & is the sole USA distributor & more,.. about this, they are Japan product all the way with nothing to hide, with many, many original Sansui/Hashimoto employees of age to know better. The amp is question is a very simple SE 27/6v6 Triode mode. I will run the Hashimoto's @ 5k. The IT's are special built by Bud Purvine from O-Netics to my op-points in circuit & are level II IT's. Surpisingly the cap coupled version of this amp I run, I like better than my 45, 300B, etc, etc. very strage, but none the less it is a happin unit @ a woppin 1w. The circuit is ridulousely simple & you can hear the simplicity,...good luck on your decision making.
J & G
Richard, et al,

I have a fairly large collection of Hashimoto iron as Isao can attest to. I would agree that the 20-watt units do have improved specs over the smaller 7-watt units I used, but at 1-2 watts output I'm not sure what, if any difference would be heard much less measured. If you have future aspirations for higher power output then perhaps the 20-watt iron is worth the extra cost.

The 45 SET amp I designed has no feedback anywhere in the design and is flat within 1dB from 25Hz to 50KHz. I purposely managed time constants and LF roll-off to reduce response to avoid large voltage swings (hence magnetic changes) in the output to handle things like rumble, warped records, etc.

I have a pair of the 3.5K primary 20-watt units which are currently in a prototype design for a 300B output stage. The 20-watt and 30-watt iron uses a difference core setup than the smaller 7-watt units, but having lived with the 45 amps for a solid year, I'm still quite content with their performance. On a seperate note, I prefer to terminate all unused winding ends on the outputs... ie, using the 5K primary tap, I terminate the winding section between 5K and 7K, same goes for the output.

Hope this helps... and good luck on your design... I'm exceptionally pleased with ALL of my Hashimoto purchases and Isao's prompt response, knowledge and close contact with the factory are an absolute plus.

Regards, KM
Hi J&H and Kmaier,

Thank you for your responses. They have definitely helped twist my arm to lash out the extra for the H-20-7U. Also, your feedback is very informative and I’m glad I was thinking along similar lines.

I was considering 2 designs for my 71A, the JE labs 71A and Joel’s latest 71A amp on this forum. This will be my first amp build after some success with a phono pre, so it’s going to be a case of slow and steady winning the race. I’m also ordering the Hl-20K-6 for a 26 preamp project.

As for Hashimoto and its distributors I have nothing but praise for Isao, his customer service is excellent and he is a pleasure to deal with.

Just one last question in regard to ordering, as there are a few company names, did you guys make payment to Optimum Business Solutions Inc?


Hi Richard,

Yes, nothing but accolades here for Isao and the Hashimoto products as well. Also, Isao bills thru OBS, so that's normal. One thing to point out regarding the Hashimoto output transformers, they are effectively inverse phase compared to others, ie, the output phase is the same as the input phase to the output tube grid. As a result, if you have a single driver stage (which inverts the phase) which drives the 71A, the output will be out of phase so you'll need to reverse the output winding (not the primary).

I recently completed a simple low-cost design for the DIY crowd... it's sitting on both Audiocircles (single driver speaker forum) and Mike's MQ forum which uses a single 12AT7 input/driver and would be excellent at driving the 71A, 45 (designed for the 45) and a 2A3 without any change. It provides a low output impedance and high output drive capability and with good tubes and iron can yield flat response to 50KHz with less than 0.5% distortion at 2-watts using a 45 with no feedback. Pics of a completed amp (using Hammond iron) with measured specs are on audiocircle.

Also, the HL-20K-6 line outputs are superb ;-) Good luck in your amp building.... hope the info here has been useful.

Regards, KM
Joined 2015
Paid Member
Sorry for resurrecting this super old thread but I am in the process of evaluating different 45's and would be interest to try ones of the type you mention.
The previous photo is not available anymore, could you possibly upload a new one with the specific structure you mention ?
I just went with Hashimoto H-20-7U for 1 watt amp, albiet it will also have O-Netics level II IT's. But will let you know how the H-20-7U sound. I should have them by next week & am ready for install. I struggled with same delima, so I flipped a coin in my head & called Isao Asakura & placed the order. Now I can relax.
J & G
Too expensive, this model are C core or EI?
His site are missing these important details.
Joined 2004
Paid Member


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Oh nice, as this core not laminated wonder what steel is this?
I have see our coleague Aldovan member are doing similar transformers for 300B.
Steel-Lab HIFI audio transformers


They ARE laminated. Can't you look at the pictures?

The non laminated cores are the amorphous ones for example.

Regarding the vibration performance: when one can spot a difference in this respect between different brands of the same tube he has got a good test amplifier but that is also a poor amplifier for listening IMHO.

An amplifier that has got best musical performance is the one that is immune as much as possible to vibrations regardless of the valve brand in use. This also means that differences between different brand in terms of vibrations is negligible.
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