Each amplifier is hand-built with point to point wiring by Dennis Had himself. Each amplifier is hand signed by him on the botom plate. Dennis considers this his form of art. Each amp is like a newly sculpted masterpiece.
He personally listens to each amplifier, both in the shop listening room and his home listening room, before it is shipped out.
This is a passion he has held for over 59 years now ever since he built his first single-ended 6V6G hi-fi amplifier for the 7th grade science fair. He never dreamed that retirement was going to be so much fun!
The QMB-25 utilizes 4x 6V6 per amp. The 6V6 is a tube that can be operated well beyond it's published specifications. It works effortlessly in this design but with authority and control. Granted it is not going to be able to drive a huge pair of low efficiency electrostatic speakers to peak demands. With regular to efficient sensitivity speakers it will provide an amazingly musical and warm sound. It is more on the neutral to warm side rather than laid back lush sounding. Most of Dennis's designs over the years have had this tonailty. The amplifier runs in Class A configiration. Class A offers a shorter simpler circuit to provide less signal deterioration. No Tube biassing is required.
The driver tube is a 6SN7. A very reliable and well reguarded tube. It is arguably the best general purpose triode tube around. What we like to call a fun tube. Lots of choices (manufacturers) to tube role with providing a different tonality. Drew's personal favorite is the Sylvania Green Label 1950's 6SN7 GTB with chrome dome.
The amplifier utilizes a 5AR4 for tube rectification. This tube essentially changes AC to DC for the power tubes to do their business. Like the 6SN7 this tube can have a good bit of difference in the tonality of the amplifier even though it is not in the signal path. Esentially it controls internal impedances when there are peak demands. It helps the amp clamp down on the speaker driver and provides the control of the sound. It affects attack, compression, dynamics and the sensitivity of the amp. It is an often forgot about piece of the puzzle. All tubes in the cisrcuit essentially lend to the end result. The better the tubes the better the sound.
* NEW Custom designed, hand wound 25 watt SE air gapped output transformers, left and right channel matched pair
* Four (4) 6V6 tubes run in a parallel single-ended class A beam power mode
* 6N7/1635 Dual Medium Mu triode driver
* Dual B+ power supplies on each amplifier ... one supply for the output tube anodes and the second B+ supply for the regulated power supply section
* Fully shunt regulated, low impedance 6V6 tube screen grid B+ power supply
* Fully shunt regulated, low impedance input tube driver, 6SL7 driver B+ power supply
* Four (4) individual R/C auto bias circuits .. one for each 6V6 output tube auto bias
* Large oil filed regulated power supply section filter cap
* Filter choke Pi-Network power supply
* Precision non-inductive metal film 3 watt resistors
* Paper and oil filed, epoxy encapsulated, coupling and by-pass capacitors
* Gold plated copper RCA input jacks
* Gold plated copper output speaker posts
* EE Teflon silver stranded 19 strand hook up wiring
* Pure 99.9% Silver Teflon Insulated internal coax interconnect
* 100% duty cycle CCS power transformer designed for 120/240 VAC 50/60 Hz primary
* .080 (12 ga) aluminum chassis and matching bottom plate
* 25 + watts per channel output with 5AR4 rectifier 20 + watts with Sophia Mesh Plate 274B rectifier ... both included for each mono
* Duty cycle of the QMB-25 MONO amplifiers is 24/7 in full operate conditions
* Frequency response @ 1 watt 15 Hz to 45 Khz +- 1 dB
* Frequency response @ 20 watts 23 Hz to 60 Khz +- 2 dB
* 61/2" wide by 13" deep and weighs 18 pounds
* Clear coat powder coat finish