Harma Valves / 12DW7/7247-HARMA STR

12DW7/7247-HARMA STR 12DW7/7247-HARMA STR Click on image(s) above to view larger

All prices contained on this page are exclusive of VAT. This is currently charged at 20% and is payable by the UK only.

A test report is available click here to view

Harma valves consist of a selected range of valves that are chosen after meeting stringent standards for sound quality and reliability. These valves are sourced from current production as well as some of the finest Nos valves available. Unlike our competitors no Harma valves, past or present has been made in China. Harma valves represent the finest available items of their type available.

Harma valves are tested using a range of custom designed and built test rigs which are unique to Watford valves.These unique tests are not offered by any other valve supplier in the world.

All Harma pre amp valves undergo the drive rating system; the valve undergoes a series of through tests under full operational conditions. This involves a controlled burn in process to ensure perfect stability and correct ageing. A shock and vibration test, microphoney, hum, and a balance and symmetry test.

All Harma output valves undergo our own unique real world burst testing. No other supplier tests valves this way. The burst testing process involves a series of varying timed electrical signal bursts. This runs the valves under the same stress conditions that they will meet in your amplifier especially when overdriven. All out put valves are then dual matched by us on anode current and gain. This will ensure that you get the best selected valves available anywhere in the world.
The Harma 12DW7 STR is based on the American dual plate design that was popular in the late 1960's. It has been designed and selected to provide high grade performance in vintage amplifiers.

The Harma 12DW7 STR features an internally rugged construction with thick mica supports. This has a number of advantages such as reduced microphonics and better isolation from vibration. This is particularly useful in large bass amplifiers such as the original Ampeg SVT and V4B.

The grids windings are all gold plated and the valve provides one of the most neutral and warmest vintage tone of all the current production types of this valve.

The 12DW7 is a dissimilar triode i.e. plate 1 is an ECC83/12AX7 plate 2 is an ECC82/12AU7 and each section is carefully selected to premium 7247 specification.

Due to the fact that it is dissimilar triode it is not a replacement for an ECC83/12AX7 type.
The other name for a 12DW7 is ECC832 referring to the two different elements

This is good news for all Ampeg SVT and V4B owners is that now you a high grade alternative to the American made 7247

All Harma preamp valves are Dynamically Drive tested under real working condition have passed the following tests:

Gain (db) Drive Tested)
Transconductance (gm) Drive Tested
Output Drive Tested
Noise 1 (signal to noise)
Noise 2 (Aural)
Microphonics Test 1(Ambient)
Microphonic Test 2 (Shock)
Cathode Test
Grid Leakage Test



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