diff --git a/stdlib/LinearAlgebra/src/tridiag.jl b/stdlib/LinearAlgebra/src/tridiag.jl
index 235fa5636877a..da15e1680f53a 100644
--- a/stdlib/LinearAlgebra/src/tridiag.jl
+++ b/stdlib/LinearAlgebra/src/tridiag.jl
@@ -70,9 +70,14 @@ julia> A[2,1]
 SymTridiagonal(dv::V, ev::V) where {T,V<:AbstractVector{T}} = SymTridiagonal{T}(dv, ev)
 SymTridiagonal{T}(dv::V, ev::V) where {T,V<:AbstractVector{T}} = SymTridiagonal{T,V}(dv, ev)
 function SymTridiagonal{T}(dv::AbstractVector, ev::AbstractVector) where {T}
-    SymTridiagonal(convert(AbstractVector{T}, dv)::AbstractVector{T},
-                   convert(AbstractVector{T}, ev)::AbstractVector{T})
+    d = convert(AbstractVector{T}, dv)::AbstractVector{T}
+    e = convert(AbstractVector{T}, ev)::AbstractVector{T}
+    typeof(d) == typeof(e) ?
+        SymTridiagonal{T}(d, e) :
+        throw(ArgumentError("diagonal vectors needed to be convertible to same type"))
 end
+SymTridiagonal(d::AbstractVector{T}, e::AbstractVector{S}) where {T,S} =
+    SymTridiagonal{promote_type(T, S)}(d, e)
 
 """
     SymTridiagonal(A::AbstractMatrix)
@@ -513,11 +518,21 @@ julia> Tridiagonal(dl, d, du)
 """
 Tridiagonal(dl::V, d::V, du::V) where {T,V<:AbstractVector{T}} = Tridiagonal{T,V}(dl, d, du)
 Tridiagonal(dl::V, d::V, du::V, du2::V) where {T,V<:AbstractVector{T}} = Tridiagonal{T,V}(dl, d, du, du2)
+Tridiagonal(dl::AbstractVector{T}, d::AbstractVector{S}, du::AbstractVector{U}) where {T,S,U} =
+    Tridiagonal{promote_type(T, S, U)}(dl, d, du)
+Tridiagonal(dl::AbstractVector{T}, d::AbstractVector{S}, du::AbstractVector{U}, du2::AbstractVector{V}) where {T,S,U,V} =
+    Tridiagonal{promote_type(T, S, U, V)}(dl, d, du, du2)
 function Tridiagonal{T}(dl::AbstractVector, d::AbstractVector, du::AbstractVector) where {T}
-    Tridiagonal(map(x->convert(AbstractVector{T}, x), (dl, d, du))...)
+    l, d, u = map(x->convert(AbstractVector{T}, x), (dl, d, du))
+    typeof(l) == typeof(d) == typeof(u) ?
+        Tridiagonal(l, d, u) :
+        throw(ArgumentError("diagonal vectors needed to be convertible to same type"))
 end
 function Tridiagonal{T}(dl::AbstractVector, d::AbstractVector, du::AbstractVector, du2::AbstractVector) where {T}
-    Tridiagonal(map(x->convert(AbstractVector{T}, x), (dl, d, du, du2))...)
+    l, d, u, u2 = map(x->convert(AbstractVector{T}, x), (dl, d, du, du2))
+    typeof(l) == typeof(d) == typeof(u) == typeof(u2) ?
+        Tridiagonal(l, d, u, u2) :
+        throw(ArgumentError("diagonal vectors needed to be convertible to same type"))
 end
 
 """
diff --git a/stdlib/LinearAlgebra/test/tridiag.jl b/stdlib/LinearAlgebra/test/tridiag.jl
index 2d846683e38c3..0c07e5b160c58 100644
--- a/stdlib/LinearAlgebra/test/tridiag.jl
+++ b/stdlib/LinearAlgebra/test/tridiag.jl
@@ -95,12 +95,12 @@ end
         @test isa(ST, SymTridiagonal{elty,Vector{elty}})
         TT = Tridiagonal{elty,Vector{elty}}(GenericArray(dl), d, GenericArray(dl))
         @test isa(TT, Tridiagonal{elty,Vector{elty}})
-        @test_throws MethodError SymTridiagonal(d, GenericArray(dl))
-        @test_throws MethodError SymTridiagonal(GenericArray(d), dl)
-        @test_throws MethodError Tridiagonal(GenericArray(dl), d, GenericArray(dl))
-        @test_throws MethodError Tridiagonal(dl, GenericArray(d), dl)
-        @test_throws MethodError SymTridiagonal{elty}(d, GenericArray(dl))
-        @test_throws MethodError Tridiagonal{elty}(GenericArray(dl), d,GenericArray(dl))
+        @test_throws ArgumentError SymTridiagonal(d, GenericArray(dl))
+        @test_throws ArgumentError SymTridiagonal(GenericArray(d), dl)
+        @test_throws ArgumentError Tridiagonal(GenericArray(dl), d, GenericArray(dl))
+        @test_throws ArgumentError Tridiagonal(dl, GenericArray(d), dl)
+        @test_throws ArgumentError SymTridiagonal{elty}(d, GenericArray(dl))
+        @test_throws ArgumentError Tridiagonal{elty}(GenericArray(dl), d,GenericArray(dl))
         STI = SymTridiagonal([1,2,3,4], [1,2,3])
         TTI = Tridiagonal([1,2,3], [1,2,3,4], [1,2,3])
         TTI2 = Tridiagonal([1,2,3], [1,2,3,4], [1,2,3], [1,2])
@@ -505,6 +505,11 @@ end
     @test SymTridiagonal([1, 2], [0])^3 == [1 0; 0 8]
 end
 
+@testset "Issue #48505" begin
+    @test SymTridiagonal([1,2,3],[4,5.0]) == [1.0 4.0 0.0; 4.0 2.0 5.0; 0.0 5.0 3.0]
+    @test Tridiagonal([1, 2], [4, 5, 1], [6.0, 7]) == [4.0 6.0 0.0; 1.0 5.0 7.0; 0.0 2.0 1.0]
+end
+
 @testset "convert for SymTridiagonal" begin
     STF32 = SymTridiagonal{Float32}(fill(1f0, 5), fill(1f0, 4))
     @test convert(SymTridiagonal{Float64}, STF32)::SymTridiagonal{Float64} == STF32