Here is a fresh build of a single ended 6550 amp featuring Edcor 15 watt SE output transformers and a Hammond power transformer and a vacuum tube rectifier for smooth sound quality and more voltage versatility. The circuit is the excellent sounding RH type which can use any of the above tubes. I have tried all of the above tubes in the circuit but my personal favorites are Mullard EL37 and Tung Sol black plate 6550. Another unique feature is the ability to change the rectifier tube from 5V4 to 5U4 and almost any other with similar pinout to vary the sound and the B+ voltage.
The amplifier circuit is call the RH Universal amp hence the ability to utilize so many different output tubes. RH amps feature Schade or plate to plate feedback from the output tube to the driver tube. This is local type feedback is less intrusive to the audio signal. KEY FEATURES
CLCLC Power Supply with FILM CAPACITORS
This means film capacitor, inductor, film capacitor, inductor, film capacitor for the all important power supply ripple removal. Inductors are preferred to large and slow electrolytic capacitors which can color the sound as well as reduce the dynamics. In that same vein, film capacitors are preferred because they can release their energy far quicker than electrolytic caps.
Why use an inductor? An inductor not only reduces the AC ripple but also acts as an energy storage device by virtue of its induced magnetic field. When current demand increases the magnetic field will supply additional current.
EDCOR OUTPUT TRANSFORMERS: I decided to install 15 watt Edcor OPTs, which are highly regarded for the excellent quality and most important excellent sound. Another plus is that these quality opts are made in the USA. Typically, OPTs take many hours to break in and these are expected to improve over the hours.
HAMMOND POWER TRANSFORMER
The power tranny is a Stout 200ma x 800v unit. Although a bit over sized for this use it runs cool to warm for a very reliable power source. CHOKE LOADED DRIVER and G2 POWER SUPPLY Adding a STANCOR choke to the driver and G2 power supply is a low tech type of stabilized current supply which is especially beneficial for screen supply circuit. The end result is a better sounding amplifier. ALL NEW PARTS AND COMPONENTS;
RESISTORS are minimum 1 Watt with quiet metal film except for 1/2 watt carbon composition in the critical input grid of the power tube. The signal capacitors are military style paper in oil in a brass tube with ceramic end seals. This type of capacitor is expensive to make but unlike other capacitors will not break down over time. Also the power supply caps are bypassed by PIO caps for even better performance. Other components used are a steel chassis, new old stock tube sockets, input and output jacks, IEC AC inlet, stainless steel or brass hardware, and rubber feet.
TUBES:
Since the buyer should decide on the output tubes that best suit their tastes the amp will be supplied with 2 USA made RCA 6V6GT, 1 5V4, and 1 GE 6SN7GTB tubes. If the buyer wishes to purchase additional power tubes please inquire.
SOUND QUALITY
I really love the sound of my single ended amps. I used to be a died in wool push pull amp devotee, but once I built my first Single Ended amp which was a simple Motorola SE EL84 stereo amp I just could not believe what I was missing with the PP amps. That missing element is a degree of realism and harmonic richness that was not portrayed by the many PP amps that I previously owned. To put it simply the sound is more involving and more natural.
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