MOD 1
When using a power mic with the HR2510, with the ALC cranked up, you will
Overdrive the Final. Two Solutions exist, Keep the ALC turned down, or
replace the final (MRF477) with a MRF497. This will cure the overdrive problem.
To pull a few more watts from the HR2510, you may replace the pre driver ,
Q134 (2SC2086) with an ECG or NTE 340. The 340 pin outs are opposite the
2SC2086 (the 2SC2086 is BCE and the 340 is ECB). Set the bias with VR112 to
70 - 80 Ma  in USB on 28.000 MHz with a 1kHz tone and the ALC set to peak.

MOD 1a
This is an improvement on MOD1. This suggests you change the MRF477 with
the MRF497, making the necessary Bias adjustments. (as in MOD 1). Then instead
of changing Q134(2SC2086), you modify the circuit to provide more Gain.
See "The Better High Power Mod" page for more info.

!!!!!ATTENTION!!!!!
The following mods [Mod 2 & Mod 3] WERE missing some 'Key' information.
With the help of a few of you out there we have solved the problem.
Thanks, Rogerbird

MOD 2
This will cure the overdrive problem and allow you to pull a a few more watts also.
The MRF477 may be replaced with a MRF455, But since it is not a TO-220
case a mounting problem exists. A piece of aluminum, 1" wide by 2" long by 1/16 "
thick may be used to mount the MRF455, Then your new heatsink may be mounted
to the chassis heatsink underneath the circuit board. Small pieces of hook up wire
must be used to connect the circuit board leads to the leads of the MRF455.
The SECRET to make this work is to STRAP the Emitter of the MRF455 to one of the mounting screws.
With the help of several people, we have found that Uniden is using this
method to cure the problem I had before.
I have found in some radio's you may need to add or change
some of the coupling capacitors to get nominal output,
But, overall this mod is cheaper than the MRF497 mod and more robust!
I have even been able to mount the MRF455 directly to the rearpanel.
Just mark and drill 2 holes to mount it.
Also for a Bias Diode you can use a 1N4001 diode, Just make sure it
is in contact with the ceramic of the final to detect its heat.
This final set-up will last forever.

MOD 3
To double the output power you must make a new circuit board, 1" by 2",
that will accommodate two final assemblies (using two MRF455).
Remove Q132, C124, C125, D164, R157, VR112, L126 and R180.
Order Duplicate parts from Uniden Parts Department.
9900 Westpoint Drive, P.O. Box 5043,  Indianapolis, IN 46250  Tel.#317-842-1036.
         The Uniden part numbers are:
         Q132 - BDBZ0529001
         C124, C125 - BCCG815615Z
         D164 - BDFY0058001
         R157 - BRFT611004Z
         VR112 - BRTY0182101
         L126 - BLDY0221001
         R180 - BRFT614704Z
The new circuit board assembly  (both new finals) must be attached to the radios large
finned heatsink. Use hookup wires to attach the input, output and ground leads of your new
board  to the junction of C126 and R180,  R158 and L135. Study the schematic carefully,
duplicate both final assemblies as per schematic. Double check everything. If you don't have
a service and repair manual, Order one through Uniden Parts.
 

The HR2510 uses low level modulation so it will never be as loud as a radio using high level
modulation (on AM only), but by turning up the AMC, and the previous mod they become
AM performers also.

The above information was created by Thomas..and edited by Rogerbird