Closely matched pair of very rare Philips/Mullard E188cc SQ.
The E188cc is also known by its American designation 7308. These Philips / Mullard E188ccs have gold plated tube pins, a frame grid, a 'dimple disc' getter, a specified lifespan of 10,000 hours, very low microphones and a very good trio balance.
According to the production code, they were both manufactured in week 4 of January 1960 in the Mullard Radio Valve Co. factory in Mitcham, England. Philips was already the owner of Mullard at that time.
The matching production code etched in the glass of both tubes is VRI R0A4, where VR stands for the type E188cc, the 1 for the batch (the so-called Change Code), the R for the Mitcham factory, the 0 for the year 1960, the A for January and the 4 for the fourth week of the month.
The quality of the relatively fragile lettering is about 80/100, the gilding of the tube pins 90/100. The tubes are used, but they measure very strong and are still perfectly balanced. Measurement on the Tube Imp Mini TT was performed with a fixed Cathode Current of ~11mA for each individual triode. On the basis of this mA, the Transconductance/GM (mA/V), the Voltage Gain (Mu) and the Plate Resistance (Ra) were measured and calculated.
Transconductance (mA/V)*
Tube 1: 9.10 / 9.18
Tube 2: 8.56 / 8.73
Voltage Gain (Mu)*
Tube 1: 34.9 / 34.6
Tube 2: 35.5 / 35.7
Plate Resistance (Ra = Mu ÷ mA/V)*
Tube 1: 3.84 / 3.77
Tube 2: 4.15 / 4.09
The match - both mutually and internally - is nominally within 5%, with a maximum difference of 8%, which can be considered Platinum Matched (≤10%). The match on Transconductance alone would be Platinum+ (≤5%).
One of the most beautiful 'drop-in' alternatives for Ecc88/6DJ8 or E88cc/6922.
The price is in accordance with comparable market prices and based on rarity, excellent measurements, very accurate match, corresponding production dates/batch numbers and good external condition of these rare and sought after tubes. The original boxes are no longer available, the tubes are therefore shipped in white tube boxes. Shipping (domestic and international) by registered mail only.
* = This is a private sale of a vintage product that is almost 60 years old. No warranty applies, no right of return. The tubes are sold 'as is'. The measurements are actual, but provided only to indicate the state of the tubes on the moment of sale.