Used amplifiers

Time to split up the special’s page into two so one for headphones and another one for electronics.  Here I’ll list what my more unusual amplifier projects, used amplifiers that I’ve refurbished/rebuilt plus any other piece I’m selling.  Feel free to contact me at spritzer@mjolnir-audio.com if you are interested in any item here.  I will reply to every mail so if you haven’t received a reply within 24 hours then feel free to send me another email.  Email gets lost all the time or is flagged as spam.  All prices in US dollars (USD).

 

Ahhh the Stax SRM-T8000. I bought this one as the first used unit to hit the market anywhere as I just had to try the new flagship amp. I got it from Japan but we quickly figured out how change to any voltage so it is now set to 240V. This is serial number 26 so early first batch for people who care about that. It is mint in every way and while Kevin Gilmore and I have both opened it up to see what the circuit contains, it is still perfect. The screws were not in the top as Stax screws always get scratched with use so they were kept secure until the amp ships out.  It comes with everything a new amp would come with except the wait time…  😉

Price: 4600$ plus shipping

This is a special KGSSHV I built a while ago and sold to the US.  The transformer developed a fault so refunded the buyer and had it sent to Kevin Gilmore who replaced the transformer for me.  The amp has been sitting there for a few weeks working great so now is time to list it.  This uses the stereo KGSSHV board and the Carbon power supply.  It runs at +/-400V and is otherwise a standard KGSSHV.  I had this spare chassis at the time so I wanted to put it to good use.  The amp is located in the US and set to 117V so I’d prefer a US buyer but it can easily be changed to 230V through the voltage selector on the inside of the chassis.  The amp is in perfect condition and looks just like these pictures which I took for the original listing.

Price:  2000$ plus shipping

 

Here is one I thought I’d never sell but then again, I never use it. So this is a Stax SRA-7S which as the first popular Stax amplifier and designed for the SR-1. This was back in 1967 so before even the SR-3 or SR-X mk1 was released. It’s an all tube design and quite small for the amount of circuitry that is in it. So I got this amp from Japan and it has been completely rebuilt. The only original parts in this as the chassis, output sockets, tube sockets, amplifier PCB and the original tubes as they all measured good. The rest is all new and improved. There is a thread on head-case.org where I documented the lengthy rebuild process but basically when I got the amp it was 100V only and the power supply was basic to say the least. There was also no place to put the improved power supply so the first thing I did was to scrap the phono input as it took up so much space and was terrible to begin with. The transformer was scrapped and a new unit from Hammond was installed with the +300/+600V power supply from the Octave. The amplifier board was completely rebuilt with far better parts and moved further away from the transformer.

I really went to town here though as everything else was changed and upgraded. The front panel markings were peeling off when I got the amp so I cloned them and had my laser shop etch them onto the same plate once I had cleaned off all the old labels. The back panel RCA sockets had not aged well so I replaced them with new gold plated Neutrik sockets and redid all of the input wiring. There was a new input switch fitted plus a new volume control and balance pot, both Alps RK27. The power and mono/stereo switches were also both replaced with new units from Japan plus one output was converted to Pro bias output to make it more modern.

This amp has one unique feature which Stax stopped adding in the 70’s… it has a tone control. Basically this is a switch which has 4 settings and it increases the amount of series resistance there is inline with the output of the amp. Now the stock configuration was odd as it treated just one half of the push pull output so when I rebuilt it, it’s done right with matched sections for each output phase. Finally the amp was fitted with new feet, a proper power cable with strain relief and the top cover was powder coated. Last but not least…the knobs used on these are still being made in Japan so I custom ordered new ones as the old ones were unsightly.

The prices for these amps are crazy in Japan now even with tatty samples hitting 1000$ or more. I paid way too much for this one and the rebuilt was…insane so that explains the high price. I also kinda don’t want to sell it but that’s how it is… 😉

Price: 1700$ plus shipping

Finally one of these is ready after a lot of delays, a fully rebuilt and modified SRM-T1.  I found a nice example in Japan of this iconic amp and had it shipped here.   I then replaced all the capacitors in the amp, modified the bias supplies to be up the latest standard and finally, installed constant current sources for the tubes.  The main issue of the T1 and all the later variants (T1S, T1W, 006t, 006tA) is how the tubes are being driven.  They have resistor current sources so a large part of the potential power is wasted in those resistors, making the amps sound a bit bland.  What I did was remove all those resistors and fit a large heatsink in their place with the same current source as used in the BHSE and KGST fixed to it.  The difference in performance is rather dramatic, the amp suddenly feels alive and something actually happens when you increase the volume.  Now I can’t change the fact that the tubes used in these aren’t ideal but this at least makes sure the potential in there isn’t wasted as heat in the resistors.

The actual amp is a late model T1 and all the amps which might have degraded with time have been replaced and the amp thoroughly tested.  It is in good over all condition with just some small paint marks on the back of the cover.  The tubes are GE which were in the amp when I got it but they test like new.  The amp has an internal voltage selector so I can set it to what ever voltage before shipping it out.

Price:  1200$ plus shipping

 

I recently had all the amps I’d been keeping in storage in Japan shipped to me and rebuilt them.  The first one is a SRM-313 which was my first Stax amp so I got this one for nostalgic reasons.  Excellent amp and this is one of the first ones (serial number 100) so it has the voltage selector on the back.  This is the first real deviation from the SRM-1 Mk2 design Stax did, it uses less power but now the output stage is more modern and thus delivers more power.  I cleaned the amp up, fixed the bias supply to make is suitable with the modern stuff and replaced the RCA inputs as they were damaged.  Otherwise it is in excellent condition.  There is no original box and it can easily be set to any voltage.

Price:  610$ plus shipping

I have two of these SRM-1 Mk2 amps.  Both are the last version with all metal film resistors though one is slightly older than the other.  These are the normal bias version so I populated the spot on the PCB for pro bias and modified one socket for Pro use.  I also replaced all the capacitors, redid the normal bias supply to make them suitable for use with modern Stax phones. Nothing more really needs to be said about this amp, it is the forefather of all modern Stax amps and they still sound excellent once they have been rebuilt.

First amp is sold so this is the slightly older amp, some marks on the chassis and some impact damage to the back panel.  It is really fragile on these amps due to the large cutout for the IEC input and the voltage selector.  Functionally it is perfect as well, offset and balance adjusted to zero and I cleaned the volume control with Deoxit do make sure it will be noise free for years to come.

Price:  500$ plus shipping

This is a one off Dynalo like the other ones I’m selling but only in a project box. This case came with some laser etched markings so I just used it as a test bed for this Dynalo design. This actual amp has the brand new matched input fets which many of the future amps will use. Only other difference is the lack of markings and just one input, no loop output. Can be set to either 117V or 230V.

Price: 510$ plus shipping

This one has been sitting around for a while, a SRD-7 Mk2 Pro bias transformer box. It can drive both normal and Pro bias headphones at the same time using pretty much any stereo amplifier. The amplifier is connected via the gray umbilical and I installed banana plugs on it to make connecting it to amps easier. It works on 100-240VAC and has a US/Japanese plug but I can supply an adapter for use in Europe.

Price: 410$ plus shipping

Last updated 20.05.18

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