Testing - Pre Amp Valves

Testing main | Testing Pre Amp Valves | Testing Output Valves

THE X-FACTOR

Watford Valves research into testing techniques has developed test rigs which test the characteristics relevant to toady's musician. We introduced Full drive testing, burst testing & high plate volt testing back in the mid 1990’s. Still to this day no other valve supplier offers valves tested in this way.

Watford Valves was the first company to introduce Cryogenic treatment on an established brand. To read more about the Harma Cryogenic range and this revolutionary treatment select the Cryogenic section from our products menu.

We also offer our own brand, the HARMA Diamond superior grade valve range; these are specially selected and tested to meet the needs of the modern working musician. The valves are sourced from high quality new old stock items as well as current production items. The valves build quality, performance; tone and reliability are major selection parameters.

Pre-amp and small signal valves selection service.

If you buy selected valves from Watford Valves you can be sure that the valves have been thoroughly tested to meet or exceed the original manufactures specification.

We have 4 options on small signal valves from all the major manufactures. These are included in the option box when available.

1-Factory selected: These valve are selected by the manufacture for example of Mullard, Philips
JJ Electronic, Electro Harmonix and valve brands such as Groove tubes and Tube amp doctor.
Watford valves run the additional testing on this valve on heaters and heater continually only.
These valves are the default position on our website

2-Drive tested super premium selected: In addition to the factory standard selection
We subject the valves to additional tests for excess internal noise on each triode, hum, gas, shock and vibration test, microphonics and gain to ensure uniform output gain and conformity. All these tests are carried out after the valve has undergone a prolonged burn in period. All Hama valves are tested in this way.

3-Balanced: In addition to the drive testing super premium testing the valve will undergo for balance and symmetry of the triodes. The tests involve the same signal velocity applied simultaneously to the both the valves plates thus to ensure perfect balance for matching or for use in the phase inverter position.

4-High gain drive tested 250
In addition to the drive testing super premium testing
The valve is selected from the batch when both parts of the triode selected to be above 250 points on our drive rating system. It is aimed at those of you who need every last ounce of gain and typically has around ½ of a db gain more than the standard item. This set is for the guitarist who wants early breakup when compared to the standard rated valve.

All Harma valves are tested this way as well as valves in all our kits and items which have balanced, driver, matched or selected designations. All Cryo valves have been specially selected except for wire ended variants. All our valve kits come in specially selected position matched sets. Audio valves when you ask for selected or matched items will be tested in the same way but will also undergo a distortion test to provide the maximum clean power.

All other valves are as factory selection and if you want these selected or matched then this will be indicated in the product options. Please enquire giving the valve type if you items are not listed and we will provide a quotation.

Drive tested ECC83/12AX7 types for the musician

The pre-amp valves are a vital link in achieving great sound from your amp.
The old adage of garbage in, garbage out is true and Watford Valves was the first company to offer a true and understandable rating service on signal valves.
In our tests we found that valves even with the same current and trans conductance (g/m) readings would amplify the signal quite differently in the same circuit. Until this time valve resellers had relied on equipment that tested signal valves one at a time at a nominal test setting. So Watford valves developed our 50 way valve characteristic tester and the drive rating system especially for musicians. This will enable them to choose either a valve which has a high gain rating to provide maximum drive to the output valves or a valve which will take longer to distort and provide a cleaner sound.

At stated earlier, under 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.

The rating system runs from 150 to 200 digital points for ECC81/12A7 types.
ECC83/12AX7 types have a rating of 220 to 249 which indicate a standard gain valve. A reading of 250-270 would indicate a high gain valve with both parts of the triode giving an output in this range this is called a DR250.
A very high gain version called DR270 which reads between 270- 300 digital points which we have supplied to customers in the past. This item is very rare and is only offered on the Harma brand. These valves are only available when we have sufficient yield from the batches so is not always available. These will be listed on our website when available.

The drive rating system in practical use

This system allows us to select through batches of valves and select the gain rating that you need whilst making them available at an affordable price.

The higher the rating the greater the gain and the earlier the valve will distort. The beauty of this system is that we can provide sets of valves that have uniformed output and gain thus eliminating valves of different or low output to give you maximum tone.
We term the driver valve to be the valve which runs the distortion channel, normally the input valve or V1 position in your amplifier. A balanced valve is normally used in the phase inverter position which supplies the signal to the output valve.

Here is a chart which will help you in choosing the valve most suitable to your Musical style.

Drive Rating System

- Rating
- Valve
- Type
- Comments
- 150-200
- ECC81/12AT7
- Low to medium
- gain generally gives a bright clear tone with fat compression suited to Fenders if you wish to maintain more head room so the amp sounds cleaner.
- 200-250
- ECC83/12AX7
- Standard
- gain generally gives good drive to the output valves with quicker overdrive. Great for all rock and blues players with cascading gain pre-amps.
- 250-300
- ECC83/12AX7
- High
- gain generally gives really big fat distortion at low settings on your pre-amp suitable for those critical driver/ first position. These provide the earliest and quickest break up Ideal for those who want early breakup such as Rock and Metal players

Rating Valve Type Comments
150-200ECC81/12AT7Low to medium gain generally gives a bright clear tone with fat compression suited to Fenders if you wish to maintain more head room so the amp sounds cleaner.
200-250ECC83/12AX7Standardgain generally gives good drive to the output valves with quicker overdrive. Great for all rock and blues players with cascading gain pre-amps.

250-300ECC83/12AX7Highgain generally gives really big fat distortion at low settings on your pre-amp suitable for those critical driver/ first position. These provide the earliest and quickest break up Ideal for those who want early breakup such as Rock and Metal players

We know you will hear the difference as our clients such as AC/DC, Brian May, Eric Clapton, Oasis, Radiohead, Manic Street Preachers, Joe Satriani, Sisters of Mercy, Thunder and Peter Gabriel will all testify as they have used our custom selection service.

Warranty- No Quibble satisfaction guaranteed!

All small signal valves and output valves carry a 3 month warranty from date of purchase except HARMA Diamond valves which carry 6 months warranty from the date of purchase. We warranty sweep valves such as Pl509 for 14 days from date of purchase.

If valves are to be returned then you need to obtain a return authorization number from us without this we cannot process your claim.

"Watford Valves, with the aid of its custom-built test rigs, puts the valves under ’real working’ conditions which is the equivalent of a hellish week with the US Navy Seals"
Ben Bartlett, Guitarist, Feb. 2001

Watford Valves "runs them through more checks than any other facility in the world"
Dave Hunter, Guitar Magazine, Nov 1999

Established by Musicians for Musicians Watford valves has become the first choice for supplying of tested, graded and guaranteed valves and components to the professional music and audio industry.

Testing - Pre Amp Valves

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