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Factors to Weigh in Your Tube Talk

We asked Jeff Welton about ROI and the role of tubes today

Jeff Welton
Jeff Welton

A recent RW ebook asked, “Have You Bought Your Last Tube?” It included a Q&A with Nautel’s Jeff Welton, a recipient of the Association of Public Radio Engineers Engineering Achievement Award and the Society of Broadcast Engineers James C. Wulliman Educator of the Year Award.

These are excerpts; read the free ebook at https://www.radioworld.com/ebooks.

 

RW: Do you find that many users are attached to their tube systems, both because of familiarity as well as cost factors? 

Welton: Very, very few — and it’s a rapidly decreasing number. 

There are some who are quite apprehensive about the cost of acquiring a new box, as it’s a big number. However, in a lot of cases, especially if you amortize it over the period of a lease or bank loan, the overall savings can actually outweigh the acquisition cost. 

I’ve had situations where a station leased a solid-state transmitter to replace a tube rig, and the savings in operating costs actually made the lease payments. Obviously that’s not always the case, but it’s something to consider, especially if the current rig is eating you out of house and home, electrically speaking!

RW: What considerations then should an engineer or manager use to assess the ROI on a new purchase?

Welton: It’s not enough to just look at purchase price. Look at the power bill now — and get the manufacturer to use that to provide you with a ballpark of what it would be with the new rig. Remember that this will just be an estimate — demand costs and overage charges can be hard to calculate without an intimate knowledge of the specific utility.

Also factor in the amount of time your engineer spends doing repairs — or if you have a contract engineer, what it’s costing in emergency calls. Don’t expect engineering costs to go away; if you’re not doing maintenance, it’s the same as owning a car and never changing the oil … it’s not if you’ll have a failure, but when. However, you can factor in the cost of emergency repairs and tube costs; those alone can make up several thousand dollars a year. 

Also look at air handling; if you’re air conditioning, you’ll need less of it as a rule. Forced air is less a concern. Obviously you should look at extra costs that may come with a new rig, also; liquid-cooled systems, for example, tend to have much higher installation costs associated with the plumbing. That’s a one-time thing, but it does need to be considered. 

If you are using air cooling, you may decide to switch from forced air to air conditioned; that’s also an impact on ROI. 

Remember that manufacturers will typically be leaning toward the solutions they provide, so get a couple of different opinions, even if you already think you know what you are leaning toward.

RW: What’s the expected life of a tube these days?

Welton: It varies, a lot. Some of the more popular systems out there are lucky to get 11 months out of a tube anymore, even with careful filament voltage management. Others are still good for a couple of years. I think the days of seeing 50,000 or more hours on a tube are pretty much gone. Part of that is systemic — the folks who know how to manage tuning for maximum tube life are slowly leaving us — and part of it seems to be related to material factors, but that’s not an area I’m proficient in, for obvious reasons.

RW: How much more efficient are solid-state designs?

Welton: For the most part, overall efficiency of a solid-state FM transmitter is around 72% these days — that’s AC to RF. For tube transmitters, efficiency can vary from less than 50% for a grounded grid design, to 65% or higher for some of the other designs, so the efficiency of a solid-state design will be somewhere between 10 and 50% higher than that of the tube system, as a rule.

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