Rohde & Schwarz 50-Watt Tube Amplifier FR501-8 Röhrenverstärker 6x EL34
This is a very interesting vintage Tube Amplifier made by Rohde & Schwarz, late 50ies. Although there is no Rohde & Schwarz branding on this unit, it was clearly made by R&S, as you can clearly see: the typical housing, parts, transformers, the fabrication techniques, the numbering, the audio transformer cans, the ceramic solder stripes, the tube sockets, the writing, the numbering, the faceplate, the handles, everything is screaming "Rohde & Schwarz". It was probably an internal lab unit, not meant to be for public, or a private project from one of the R&S engineers, using all the R&S tools and the R&S shop floor.
It is called "Ultraschallverstärker" (german for Ultrasonic amplifier). Ultrasonic is the term for frequencies that are higher than what the human ear can hear. So this amplifier was originally made for frequencies above 20kHz. But wait.
The amplifier has a large metal core output transformer (the one in the middle). Considering the extreme size of the core I can only imagine it can do audio frequencies aswell and might go really deep. And considering the amount of pentodes the unit should have a lot of power. Some other tube amplifiers have problems with higher frequencies, this should not be a problem on this unit, since it is made for ultrasonic waves. Chances are it has a RC-filter that cuts off everything below 20kHz. There is no schematic available, so this is not for starters.
Somewhen within the last 20 or 30 years, an unknown hobyyist installed a transitorized EQ amplifier, which is powered by another small PCB with a plastic covered EI-transformer. Some input and output connectors were added to the faceplate. To be clear: This unit is not original anymore.
It has outputs for:
2.5 Ohm
5 Ohm
10 Ohm
20 Ohm
80 Ohm
The output may come from 6 pentodes of type EL34. Not sure if all of them are in the power amplifier section. Chances are some of them are for voltage regulation.
I did not test or powered up the amplifier. I don't know if it's working or not. I don't know if it's capable of the full audio spectrum, down to 20Hz, without modifications. This is a wonderful unit, with a powerful and really high quality metal M-Core output transformer. I don't believe it is necessary to change it to a more audio-ish model. This unit is worth any look. I highly recommend to spend some time with it. With 20.000 items on stock, I can't spend more than making pictures and offering online.
There is a test switch to test each and every tube on the built-in VU-Meter, which functions as a tube tester in this mode.
If you consider to buy, please ask for the full set of photos. There is a total of 47 photos available, but I can only upload 15 of them on the WIX shopping platform.
To be clear: this unit is mono. It has lots of rust on the housing. It is untested and could potentially be non-functional. There is no melted transformer or such things, nothing obvious, and I'm also willing to perform some smaller tests for you. Everything that can be measured by using a multimeter, without powering up the unit, can be done upon request (at no additional charge). I am willing to video-phone with you. There is no power cable included, and I don't have a manual or schematics. This unit is not rocket science, it's a simple analog tube amplifier, but nothing for starters either. Please note that it is not recommended to power up such an old device without changing - or atleast testing - the power caps in the PSU prior to that. The tubes are untested and might be low.
The power supply consits of a large power transformer (probably M-Core) and a DC-coil, and two Siemens caps, each of 100+100uF 385V.
Audio transformers: there are two shielded cans which are most like audio transformers (small signal level), and there is the large output transformer in the middle, which has tons of different outputs.
There is a small (modern) power supply for the equalizer. You can either use it or remove it together with the EQ PCB.
Before you buy or send me the total, please aks me for the exact shipping fee. In this case I can't calcualte the correct shipping fee on the WIX platform, because it is too difficult. Some postal countries have restriction on the total shipping weight (i.e.20kg). But this unit has more than 30kg. I have to ship the housing and the main unit in two different boxes. If your country is restricted by postal office weight limits, we have to discuss different possibilities: an optional courier that doesn't mind the high weight (most like more expensive), a small pallette (expensive), local pickup (prefered), or to remove the power transformer and ship it separate. All of these solutions are at an additional costs.
Price is fixed.
TECHNICAL AND COSMETIC CONDITION: This unit is untested and therefore sold as "untested". Since untested items could be either working or faulty or anything in between, they are always sold as "faulty / AS-IS". But you are welcome to collect in person and test the item PRIOR to your purchase here at my store (please come with anything needed for a complete test). However, there is no such thing as a warranty and returns on this item. Since there are so many items on stock (over 20.000), I simply can't afford to test all of them, and also they are really old. The price already reflects the worst possible case. Please see the photos. I did my best to picture and describe my items, but that's not a complete report, and not a certificate that everything is proper and complete. Functions that partially worked on the pictures may or may not work on the next power-up. If anything is missing on my photos that you think it should be included, or WAS included back then when it was originally sold, then well: it's not included. If it's not pictured in the photos and not mentioned in the description, then I don't have it. This offer is meant for collectors, hobbyists, and/or engineers only, who are able to fix technical problems and missing parts by themselves. This unit might or might not need a repair. It might or might not do what you want. It might be out of alignment or even completly 'silent' at all. It might not power up. You are buying an old product that might need some service and/or a repair. Cosmetics: Unless otherwise stated, the pictures show the cosmetic condition of the item you get. I am willing to do a video-call with you, right next to your desired item, to end all doubts and to answer all of your questions. If there are multiple items available, "tears and wears" seen on the photos might be on a different spot, but they are kinda equally in number and size.