I haven't heard of any problems with the 6.2 meter, Amyemiline. If you are happy with the brand of UVB lamp you are using, and know what distance you need it to be... i.e., you just want to monitor its decay, then a Solarmeter 6.2 is fine, and will do the job well.
But if you want to compare lamp types and lamp brands, or compare lamp readings with sunlight, it is a very difficult meter to use. This is because it doesn't measure just the wavelengths that enable vitamin D synthesis and cause sunburn, which are the shorter UVB wavelengths that the 6.5 measures. The 6.2 ALSO measures long-wavelength UVB and a little UVA. And because sunlight has a lot more of these than a UVB fluorescent tube, and a UVB fluorescent tube has a lot more than a mercury vapour lamp... well, this means that in terms of "sunburn strength", a reading of (for example) 100uW/cm2 on a Solarmeter 6.2 is not very strong UV in sunlight, but can mean quite strong UV from a tube and very strong UV from a mercury vapour lamp....
(I wish this was easier to explain... :? )
Personally, in your position I'd sit it out, and get your new 6.5 fitted with the proper replacement filter cap....
But if you want to compare lamp types and lamp brands, or compare lamp readings with sunlight, it is a very difficult meter to use. This is because it doesn't measure just the wavelengths that enable vitamin D synthesis and cause sunburn, which are the shorter UVB wavelengths that the 6.5 measures. The 6.2 ALSO measures long-wavelength UVB and a little UVA. And because sunlight has a lot more of these than a UVB fluorescent tube, and a UVB fluorescent tube has a lot more than a mercury vapour lamp... well, this means that in terms of "sunburn strength", a reading of (for example) 100uW/cm2 on a Solarmeter 6.2 is not very strong UV in sunlight, but can mean quite strong UV from a tube and very strong UV from a mercury vapour lamp....
(I wish this was easier to explain... :? )
Personally, in your position I'd sit it out, and get your new 6.5 fitted with the proper replacement filter cap....