GU74B/4CX800A VACUUM TUBES
Vine is the world's premier supplier of fully tested guaranteed GU74B vacuum tubes. These tubes are used in many commercial amplifiers such as all the ACOM amplifiers, and amplifiers from Alpha Power, Command Technologies, and several other manufacturers. These tubes are NOS (New old stock) that are sourced through our contacts in Eastern Europe. Our service engineer has built a special tube tester for the GU74B, which tests it by applying different values of grid bias at a fixed screen and anode voltage. Please see the pictures below. As well as performing the dynamic performance tests we also apply a "gas" test and reject any tube that does not pass it. We also put every tube through an RF test in an ACOM amplifier. Please see the pictures of our tester, as below.
Our tests give anode current plotted against different values of grid bias and recorded. Every tube we sell comes with a certificate of conformity showing the tester results. We also test every tube in an ACOM1010 amplifier on three bands to ensure that RF performance is acceptable. As far as we know we are the only tube supplier to make tubes available that have been tested in this way, and with documented evidence of performance. From a large quantity of tube tests, we are then able to select individual tubes with close results and set them aside as matched pairs.
Because prices we have to pay vary, and have been increasing recently, we cannot publish a price for our tubes on this web page. Please contact us for prices and availability. We are able to ship worldwide at reasonable cost.
There has been considerable interest in our tube stocks, so we have prepared the following Frequently Asked Questions / Answers.
Q1. Is there a world shortage of GU74B tubes?
A1- Not that we can see, but everyone is having to pay more for them, particularly as some have been unwise and have started a "scarcity" rumor. Those sitting on stocks in Eastern Europe have heard about the rumors and have put the prices up.
Q2. Is Svetlana still making these tubes?
A2. Yes, production has started again, but prices are going to be significantly more than for NOS tubes.
Q3. Are the tubes in Vine's stock new or NOS (New Old Stock)?
A2. All of ours are NOS tubes. We don't know anywhere where you can get new tubes as such. Some say the NOS tubes are better anyway. All the tubes in current-production amplifiers are NOS tubes and seem to be fine.
Q4. Do you offer a warranty with your tubes?
A4. Of course, but as we have no control over the conditions under which they are used, we are prepared only to offer a 30-day warranty. The deal on the warranty is that if you find a tube we send you is bad, you send it back at your expense, then we send to you (shipping prepaid) one at our expense.
Q5. How can you justify asking more for your tubes than the cheaper ones I see on eBay for instance?
A6. We test and guarantee our tubes. You also know where we are! If you buy a dud on eBay (around 10% of the tubes we receive are rejected in our testing process) you may have great difficulty getting any remedy. We stand by our reputation for service support. Remember too that designing our tube tester and building it was expensive, and also that we have to expect some proportion of bad tubes from our suppliers. These factors have had to be built into pricing.
A6. How exactly are your tubes tested?
Q7. We have a tube tester specifically designed to test the GU74B tube. 1500V EHT and 340 screen volts are applied to the tube, Varying levels of control grid bias are applied through a switched network. We measure the anode current flow and have pass / fail parameters for the tube. We log the grid / anode characteristics for this set-up for each step of grid bias applied. Some tubes will give very close results to other tubes. We put these aside to sell as matched pairs. In addition to the DC test regime provided by our tester, all tubes are also tested in an ACOM1010 amplifier to ensure that RF performance is acceptable. As part of the testing procedure, a certificate of conformance is generated where we log the results of our tests. This certificate accompanies all tubes sold.
Q8 How much are the tubes?
A8. Unfortunately we cannot give you a standard response to this. We have to pay different prices for them, and that reflects our selling price. We will advise you at the time you enquire.
Q9. What about shipping costs?
A9. To the USA, it costs about $35 to ship one tube/ $50 for two. Sorry but we cannot find a cheaper way that gets a signature on receipt. To European destinations it costs about EUR 15 and in the UK, pounds 10 (single tubes). Weight steps for packages vary depending on destination but it is nearly always possible to ship two or four tubes for the same shipping price as two. If your order is for multiple tubes, we will research and offer you the best shipping deal.
Q10. How can I pay for tubes?
A10. We prefer bank transfer payments but internationally that is sometimes complex. We will take MC and VISA but we impose strict security checks before shipping and we will not under any circumstances ship to addresses other than the address to which the card account is sent. We regret we do not accept credit cards for sales outside the European Community countries and USA / Canada. We will accept Paypal, which is perhaps the easiest method. However, Paypal charges are absurdly high. They charge on average a 5% handling fee and then use an exchange rate totally favourable to them. We only accept Paypal payments with a 7% addition to the total, sorry
Q11. When can I get mine?
A11. Response has been overwhelming and we are dealing with orders strictly in the sequence in which they are received. We have ordered a large quantity of tubes to supplement our stocks. We will keep you advised once you have placed an order. We do not ask for payment until we are ready to ship.
Q12. Who are you, and how can I contact you?
A12. We’re Vine Antennas Ltd. We are the UK rep for ACOM, M2, SteppIR, Optibeam and many other good things. We have been in business for 14 years. Contact may be by email – email@example.com. By fax +44 1691 831386 and by phone +44 1691 831111. If contacting us by phone please try to schedule it so that it is during the working day here, taking account of time differences worldwide.