I thought it would be interesting to do a comparison between the two types of transmitters, both AM and FM. I have been doing this thing for 25 years and have quite a bit of experience working on all types of transmitters. Some of the broadcast transmitters I have personally worked on over the years include:
- Harris: FM-20H, FM-5G, HT-35, HT-10, HT-3.5, FM-25K, FM-5K, Z5-CD, MW-50A, MW-50B, MW-1A, MW-5A, BC-5H, SX-5, SX-1A, Gates 1
- Broadcast Electronics: FM-5B, FM 3.5A, FM5A, FM30A, FM35A, FM30T, FM20T, FM10S, FM5C, FM1C, AM10A, AM6A, AM5E, AM1A
- Continental Electronics: 816R-2, 814R-1
- Collins Rockwell: 831F-1, 838E-1
- Nautel: ND-1, ND-5, XL-60, V-40, V-10, V-7.5, NV-40
- Gates: BC5P, BC1T, FM5B
- General Electric: BTA-25
- RCA: FM20ES1, BTA5J, BTA1-AR
- CSI/CCA, Visual, Energy Onix, Bauer, McMartin, QEI, some Italian something or other, etc. Various makes and models.
I think I have a fair amount of transmitter experience under my belt. What I have found is that certain brands of transmitters are better than others, regardless of whether they are tube or solid state. There are several differences in each type, obviously. As to some blanket statement about which is better, solid state or tube, I don’t have one. My statement would be “It depends.”
Tube transmitters are more rugged and will take more abuse than a solid state unit. Things like heat, lightning, EMP, mismatched antenna won’t phase a well designed, well manufactured tube transmitter. On the other hand, they are less efficient AC to RF, have higher B+ voltages, have hard failure modes, and are more difficult to linearize, if that is required for some reason.
Solid state transmitters are more broadbanded, easier to change frequency, they have soft failure mode due to redundant amplifiers and power supplies. The voltages are lower, thus they are safer to work on.
Here is a complete list of advantages and disadvantages of each type:
| Attribute | Tube | Solid State | Comment |
| Ruggedness | Very rugged, able to take heat, EMP, lightning, mistuned antenna, poor operating environment, etc | Not heat tolerant, lightning and EMP can damage MOSFETS, switching power supplies sensitive to AC mains issues | Advantage: Tube |
| Electrical Efficiency | Less efficient | More efficient | Advantage: Solid State, however efficiency gain can be wiped out due to larger air conditioning requirement |
| Failure mode | Hard, most often | Soft, most often | Advantage: Solid State, failure of a single module or power supply generally will not take unit off the air |
| Frequency agility | Difficult | Easy | Advantage: FM Solid state transmitters can easily be moved. AM transmitters still require extensive retuning. |
| Re-occurring cost | More | Less | Advantage: Solid State, as tube changes are required every two to three years |
| Maintenance | Same | Same | Advantage: neither |
| Servicing | Requires skilled engineers to service and trouble shoot | Modules and power supplies are often hot swappable and returned to manufacture for repair | Advantage: Solid State, however either type requires occasional measurements with specialized test equipment |
| Servicing safety | High voltages, contact will be fatal | Lower voltages, but can still be fatal | Advantage: Solid State |
| Redundancy | Low | High | Advantage: Solid State, multiple power amps and power supplies give solid state units more redundancy |
| Cost | Less | More | Advantage: Dependant on TPO, Higher powered solid state transmitters are much more expensive than there tube type counterparts |
| Availability | Good used market, some new FM transmitters still being built | Good new and used | Advantage: Tube |
| Reliability | Dependent on brand | Dependent on brand | Advantage: neither |
For some reason, the latest Broadcast Electronics tube type transmitters seem to have very long tube life. I installed an FM20T at WYJB in Albany, New York, in early 2001 and it is still on the original tube, some ten years later. Same can be said for the 2005 FM20T and FM30T installation at WHHZ/WKZY, Gainesville, Florida. Those tubes shows no sign of giving up anytime soon. I don’t know if that is an unusual trait of the transmitter or that particular tube.
WKZY, Gainesville, Florida
The above comparison seems to heavily favor a solid state transmitter. As a general rule, brand new solid state transmitters both AM and FM have advantages in almost every category except high power FM transmitters, where tube types still make sense. From a used transmitter standpoint, there is nothing wrong with a tube type transmitter, provided it has a solid state IPA. I have noticed the 4CX250B driver tubes most often used in FM IPA stages have markedly reduced reliability of late. I would also tend away from transmitter makes and models where the manufacture is no longer in business or no longer supports the product.
Well that answers my question
Thanks Paul.
No worries, Rob, it is what we are here for
Paul – You raise some valuable insights here of solid-state-vs tube technology in FM transmitters. I had the same discussion with an associate earlier around a 100kW AM rig (Continental 317 C3) here in South Africa – High Power AM’s of this order generally are not cheap to run and this particular plant needs a new batch of 4-400s and 4CX35,000A’s to bring the plant back to its rated spec. I’m sure the cost of a solid state plant can be recovered in the power cost/tubes that these guys will spend on the 317′s
Vaughan, They could save quite a bit of money in operating expense (tubes and electric) by switching to solid state. Nautel makes 100 and 200 MF transmitters, although I’ve never worked on one of those. The most powerful MF transmitter I’ve worked on is a Nautel XL-60, which is a good unit. Last I installed one, a 4CX35,000 was near $9,000 USD, but that goes back several years.
Of all the transmitters you have dealt with ,both AM and FM,tube and solid state,which have you found to be most reliable? Least reliable?
Dewey, good question. Are you trying to get me in some type of trouble? I would have to say I prefer the Nautel transmitters , they are top notch and the Nautel service people are on the ball. Second to that, the BE AM solid state and FM tube units are very good performers. There are many BE FMxxA and B series tube units that are still in service as main transmitters after 25 years. I also like the Continental 816 series transmitters. Those would be my top three.
Then there is everyone else. As far as least reliable, I’m not going to go too far down that road, other that to say the Harris MW50 series transmitters were one of the quirkiest boxes I’ve ever had to deal with.
Nope,…not trying to get anyone in trouble. I was just curious as to which transmitters you liked,and/or preferred the most,… and which you disliked the most and why. Though I am in the Amateur Radio Service,I still enjoy your site on commercial broadcast radio. I,too,have been bitten by the radio bug. If I were in your field of work,I would also have to most likely choose Continental 816 boxes as well,with Nautel being second to them. Haven’t read up enough on BE units to be familiar with them.Being a ham,I would have to go with an old GE 1 kw unit or a Gates 1 kw unit. Back on the subject,I wanted you to know I really did enjoy reading the article and found it very interesting.
Paul – I represent Nautel in Southern Africa and have installed their VS1 and VS300 for customers over here. I’ve done some real ‘listening’ to FM exciters over the years and really liked the FX50. It is an excellent sounding exciter. However, I think Nautel have excelled themselves with the VS series and its an outstanding unit.
Wondering if you could possibly help – I’m in process of doing a cost of ownership comparison between a tube 50kW (Continental 317C3 or similar) and solid state transmitter. Would you have access to power consumption and heat load figures for the 317C3 on hand…?
Vaughan, I agree with you on the FX-50 exciter, they are well designed units. The Nautel M-50 and I can’t remember the name of the exciter in the V-40 transmitter also sound very good. Nautel knows what they are doing.
Regarding the 317C transmitter, that is one of the few that I have not personally taken care of. I know the Dougherty transmitters were pretty efficient for tube types, somewhere in the neighborhood of 73-75% in the amplifier stage. For a 50 KW carrier, that amounts to about 67,000 watts AC, thus there’d be about 17,000 watts waste heat without modulation. Depending on the density of the modulation, that figure could easily double or more.
As far as the overall transmitter efficiency, you have to take into account the tube filaments, the blower motor, etc. I’d put the over all efficiency somewhere around 55-60%, which is a common figure for all late model tube type AM transmitters.
Thanks Paul – The VS Transmitter performance is modelled around the NVE Exciter which is integrated into the NV Series. The features of the VS are certainly unprecedented in the industry and I have customers reviewing their prized digital exciters to replace with a VS Series.
Hi Sir Paul, may I ask if you have experience or heard about Quark Electronics from Italy? and RVR also from Italy? Both of them are solid-state now, which do you think is better? Thanks
Cliff, I have heard of RVR, we had a 1000 watt RVR unit being used as an IPA in a Harris FM25K unit. Not heard of or seen Quark Electronics. Generally solid state units are the way to go, especially on high power AM stations.
This is a great comparison. Thank you for this. One thing that was not touched on was the sound quality of Tube vs Solid state. I have listened to various radio stations and have heard a significant difference in sound quality. Some have a narrow sound where some sound more full. One station that I listened to, I know has a tube transmitter and it really has a nice full sound. Any information you could provide on sound quality between the two technologies would be appreciated. Thank you.
@CDN, sound quality is a very subjective term. Tuning, inter stage bandwidth, antenna bandwidth all effect the quality of a station’s sound. Assuming that there are no issues with the transmitter or antenna, an FM transmitter will sound the same whether tube or solid state. For AM transmitters, solid state units have better fidelity, that is to say, the transmitted waveform will remain more or less faithful or the same as the audio input. With tube transmitters (and other tube audio gear) there is a certain amount of harmonic distortion added by tubes which the human ear perceives as “warmth” or “fatness” which is pleasing for most who hear it. Thus, many broadcast audio processors have some type of fatness settings to mimic this. Of course, ersatz tube sound is no substitute for the real thing
Please can some one out there outline the tube and solid state transmitters advantages and disadvantages for high power short wave transmitter?
steve
Stephen, I have little or no experience with HF broadcast transmitters, however, they are similar in form and function as AM aka MF/MW transmitters. Thus, I would put forth the following:
AM tube transmitters are rugged but less efficient that solid state counterparts. Older tube transmitters may not have spare parts. AM solid state transmitters are more efficient, but also more expensive. Also, some brands of transmitter are more complicated and require a higher level of understanding than others.
Continental HF transmitters have Solid State Modulators (SSM) which are standard with all new transmitters and I believe available as retro-fit for older models.
If money where no object, I would go for the solid state unit.