Archive for the ‘Amps’ Category

How do we test and evaluate our valves [tubes] ??

June 4, 2011

Let me say from the outset that I am NOT a valve [tube] discounter. You cannot possibly sell valves at some of the prices I have seen on-line [on Ebay, for example] with any degree of quality-control. The mark-up just isn’t there to support or justify this. It is actually quite time-consuming to test and evaluate a batch of valves.

However, I DO supply and install valves as part of my amp servicing business and also obviously with my own Richards amp custom-builds. I also supply some music shops with pre-tested and selected valves for their in-house repairs and customer sales, at prices which reflect the value-add, including quality-control and warranty.

So, how do we carry out this testing and selection of valves ? Firstly, there are very few dedicated valve-testers on the market at all, let alone devices which will test valves at realistic voltages, and/or under load. The older valve-testers which were primarily intended for testing Radio/TV valves applied relatively low voltages to the valves, which doesn’t help us much in the world of guitar amps, where voltages of between 300V and 500V DC are most common. So basically, I was forced to design and build my own valve test sets, to suit the purpose at hand.

My most expensive test equipment acquisition (apart from the oscilloscope) is the VTV [Vacuum Tube Valley] Valve Characteriser, which tests and evaluates miniature 9-pin dual-triode preamp valves, including such common types as the 12AX7 [ECC83], 12AT7 [ECC81], and 12AU7 [ECC82]. Parameters under test include gain, noise and microphony, as well as the ability to select matched triodes. This device from VTV is no longer in production. This is the device shown in the first two photo’s.

The other item shown in the third and fourth photo’s is an in-house, purpose-built rectifier valve tester, which tests both octal and miniature 9-pin rectifiers at high voltage, and under-load. Rectifier types include the commonly used 5Y3, 5U4 and 5AR4/GZ34 octal types, and the EZ81/6CA4 miniature 9-pin types, and also some more obscure types. As you can clearly see in the 3rd photo, this JJ-brand 5AR4/GZ34 is delivering 478V DC when lightly loaded.

In addition to the above test gear, I also have purpose-built testers [not pictured] for the miniature 9-pin 6BQ5/EL84 power output valves, which tests the valves at a reasonably high 390V DC, and lastly a tester for octal valves including the familiar 6CA7/EL34/6V6/6L6/KT66/6550/KT88 types, which tests the valves at the commonly used 460V DC. You can see that these testers look pretty low-tech !! I basically used whatever transformers I had leftover from servicing that would supply sufficient voltage and current for the job.

Well, that’s the BLOG for this week, hopefully we will have something different and interesting to talk about next week. Please visit us again on a regular basis !

Introduction.

April 18, 2011

HI !     This is Ivan Richards and I am now inroducing myself for the first time on my new BLOG.

I come from a musical family going back several generations. My great grand-parents emigrated from London, England to set up in Sydney as music and singing teachers. My dad, Jack Richards, held down some of Australia’s top pro guitar gigs during the 40’s and 50’s, co-founded Sydney’s first specialist guitar shop (Guitar City), was responsible for arguably the world’s first production pedal steel guitar (Kord King), most definitely played the first pedal-steel in Australia, and is the Godfather of Aussie pedal-steel.

My obsession with all things to do with music and audio electronics began in High School where I was exposed to the guitar music boom of the 60’s and was influenced by some slightly older pupils at that school who had become very sophisticated in the field of electronics to the extent of creating an in-house radio station. I couldn’t wait to finish school and start learning some practical hands-on stuff. I joined the then PMG Department, later known as Telecom/Telstra as a technician-in training and became part of the last generation to be trained in vacuum tube (valve) technology, which was still in widespread use. This training was to become invaluable later. I had access to cupboards full of valves, resistors & capacitors and started trying to build my own guitar amplifiers. I worked my way through the technical career structure, qualifying as a Technican (Telecommunications), then being appointed to positions including Technical Officer, Senior Technical Officer, Technical Specialist/Designer of Audio & Data Services (Analogue & Digital), Customer Project Manager. During all this time I was operating my amplifier business from home, after-hours, and building up a customer base as well as accumulating years of hands-on experience. When the opportunity arose I left Telstra and became a full-time musician and amp tech.

So that brings us up to April 2011 !  Apart from gigging professionally (guitar & vocals) based here in Gosford NSW,  I operate my own one-man workshop specialising in the repair, restoration, modification and custom design/manufacture of valve (tube) musical instrument amplification. I also design and manufacture a range of analogue guitar FX and splitter/signal routing pedals. I am pleased to say that my pedals have been purchased and are being used by the creme de la creme of the Aussie contemporary music scene.

I have been servicing valve (tube) audio equipment now for over 30 years and have worked on most brands and models from the late 50’s/early 60’s to current production. I can restore your amp to correct and original working order, removing unwanted and often dubious modifications and correcting previous servicing mistakes and poor workmanship. I also service some solid-state equipment, please contact me for details.

Quality workmanship and components will always be my first priority, with a strong emphasis on electrical safety.

I have also been playing guitar in bands and duos for over 30 years and have always designed, built and used my own amps and pedals. All this experience has given me the edge when it comes to working on your gear !!

Ivan.